Sokoban

Demonstrate how to find a solution to a given Sokoban level. For the purpose of this task (formally, a PSPACE-complete problem) any method may be used. However a move-optimal or push-optimal (or any other -optimal) solutions is preferred.

Sokoban levels are usually stored as a character array where

space is an empty square
# is a wall
@ is the player
$ is a box
. is a goal
+ is the player on a goal
* is a box on a goal

Sokoban solutions are usually stored in the LURD format, where lowercase l, u, r and d represent a move in that (left, up, right, down) direction and capital LURD represents a push.

Please state if you use some other format for either the input or output, and why.

For more information, see the Sokoban wiki.

C

Long, long, long C99 code (plus GNU C nested functions). Doesn't output the movement keys, instead it animates the sequence for you. Solution is move optimized. For an even longer solution, see Sokoban/C. <lang c>#include <stdio.h>

include <stdlib.h>
include <string.h>
include <unistd.h>
include <stdint.h>
include <assert.h>
include <stdbool.h>

int w, h, n_boxes; uint8_t *board, *goals, *live;

typedef uint16_t cidx_t; typedef uint32_t hash_t;

/* board configuration is represented by an array of cell indices

  of player and boxes */

typedef struct state_t state_t;

struct state_t { // variable length hash_t h; state_t *prev, *next, *qnext; cidx_t c[]; };

size_t state_size, block_size = 32; state_t *block_root, *block_head;

inline state_t* newstate(state_t *parent) { inline state_t* next_of(state_t *s) { return (void*)((uint8_t*)s + state_size); }

state_t *ptr; if (!block_head) { block_size *= 2; state_t *p = malloc(block_size * state_size); assert(p); p->next = block_root; block_root = p; ptr = (void*)((uint8_t*)p + state_size * block_size); p = block_head = next_of(p); state_t *q; for (q = next_of(p); q < ptr; p = q, q = next_of(q)) p->next = q; p->next = NULL; }

ptr = block_head; block_head = block_head->next;

ptr->prev = parent; ptr->h = 0; return ptr; }

inline void unnewstate(state_t *p) { p->next = block_head; block_head = p; }

enum { space, wall, player, box };

define E "\033["

const char * const glyph1[] = { " ", "#", E"31m@"E"m", E"33m$"E"m"}; const char * const glyph2[] = { E"32m."E"m", "#", E"32m@"E"m", E"32m$"E"m"};

undef E

// mark up positions where a box definitely should not be void mark_live(const int c) { const int y = c / w, x = c % w; if (live[c]) return;

live[c] = 1; if (y > 1 && board[c - w] != wall && board[c - w * 2] != wall) mark_live(c - w); if (y < h - 2 && board[c + w] != wall && board[c + w * 2] != wall) mark_live(c + w); if (x > 1 && board[c - 1] != wall && board[c - 2] != wall) mark_live(c - 1); if (x < w - 2 && board[c + 1] != wall && board[c + 2] != wall) mark_live(c + 1); }

state_t *parse_board(const int y, const int x, const char *s) { w = x, h = y; board = calloc(w * h, sizeof(uint8_t)); assert(board); goals = calloc(w * h, sizeof(uint8_t)); assert(goals); live = calloc(w * h, sizeof(uint8_t)); assert(live);

n_boxes = 0; for (int i = 0; s[i]; i++) { switch(s[i]) { case '#': board[i] = wall; continue;

case '.': // fallthrough case '+': goals[i] = 1; // fallthrough case '@': continue;

case '*': goals[i] = 1; // fallthrough case '$': n_boxes++; continue; default: continue; } }

const int is = sizeof(int); state_size = (sizeof(state_t) + (1 + n_boxes) * sizeof(cidx_t) + is - 1) / is * is;

state_t *state = newstate(NULL);

for (int i = 0, j = 0; i < w * h; i++) { if (goals[i]) mark_live(i); if (s[i] == '$' || s[i] == '*') state->c[++j] = i; else if (s[i] == '@' || s[i] == '+') state->c[0] = i; }

return state; }

void show_board(const state_t *s) { unsigned char b[w * h]; memcpy(b, board, w * h);

b[ s->c[0] ] = player; for (int i = 1; i <= n_boxes; i++) b[ s->c[i] ] = box;

for (int i = 0; i < w * h; i++) { printf((goals[i] ? glyph2 : glyph1)[ b[i] ]); if (! ((1 + i) % w)) putchar('\n'); } }

// K&R hash function inline void hash(state_t *s) { if (!s->h) { register hash_t ha = 0; cidx_t *p = s->c; for (int i = 0; i <= n_boxes; i++) ha = p[i] + 31 * ha; s->h = ha; } }

state_t **buckets; hash_t hash_size, fill_limit, filled;

void extend_table() { int old_size = hash_size;

if (!old_size) { hash_size = 1024; filled = 0; fill_limit = hash_size * 3 / 4; // 0.75 load factor } else { hash_size *= 2; fill_limit *= 2; }

buckets = realloc(buckets, sizeof(state_t*) * hash_size); assert(buckets);

// rehash memset(buckets + old_size, 0, sizeof(state_t*) * (hash_size - old_size));

const hash_t bits = hash_size - 1; for (int i = 0; i < old_size; i++) { state_t *head = buckets[i]; buckets[i] = NULL; while (head) { state_t *next = head->next; const int j = head->h & bits; head->next = buckets[j]; buckets[j] = head; head = next; } } }

state_t *lookup(state_t *s) { hash(s); state_t *f = buckets[s->h & (hash_size - 1)]; for (; f; f = f->next) { if (//(f->h == s->h) && !memcmp(s->c, f->c, sizeof(cidx_t) * (1 + n_boxes))) break; }

return f; }

bool add_to_table(state_t *s) { if (lookup(s)) { unnewstate(s); return false; }

if (filled++ >= fill_limit) extend_table();

hash_t i = s->h & (hash_size - 1);

s->next = buckets[i]; buckets[i] = s; return true; }

bool success(const state_t *s) { for (int i = 1; i <= n_boxes; i++) if (!goals[s->c[i]]) return false; return true; }

state_t *move_me(state_t *s, const int dy, const int dx) { const int y = s->c[0] / w; const int x = s->c[0] % w; const int y1 = y + dy; const int x1 = x + dx; const int c1 = y1 * w + x1;

if (y1 < 0 || y1 > h || x1 < 0 || x1 > w || board[c1] == wall) return NULL;

int at_box = 0; for (int i = 1; i <= n_boxes; i++) { if (s->c[i] == c1) { at_box = i; break; } }

int c2; if (at_box) { c2 = c1 + dy * w + dx; if (board[c2] == wall || !live[c2]) return NULL; for (int i = 1; i <= n_boxes; i++) if (s->c[i] == c2) return NULL; }

state_t *n = newstate(s); memcpy(n->c + 1, s->c + 1, sizeof(cidx_t) * n_boxes);

cidx_t *p = n->c; p[0] = c1;

if (at_box) p[at_box] = c2;

// leet bubble sort for (int i = n_boxes; --i; ) { cidx_t t = 0; for (int j = 1; j < i; j++) { if (p[j] > p[j + 1]) t = p[j], p[j] = p[j+1], p[j+1] = t; } if (!t) break; }

return n; }

state_t *next_level, *done;

bool queue_move(state_t *s) { if (!s || !add_to_table(s)) return false;

if (success(s)) { puts("\nSuccess!"); done = s; return true; }

s->qnext = next_level; next_level = s; return false; }

bool do_move(state_t *s) { return queue_move(move_me(s, 1, 0)) || queue_move(move_me(s, -1, 0)) || queue_move(move_me(s, 0, 1)) || queue_move(move_me(s, 0, -1)); }

void show_moves(const state_t *s) { if (s->prev) show_moves(s->prev); usleep(200000); printf("\033[H"); show_board(s); }

int main() { state_t *s = parse_board(

define BIG 0

if BIG == 0

8, 7, "#######" "# #" "# #" "#. # #" "#. $$ #" "#.$$ #" "#.# @#" "#######"

elif BIG == 1

5, 13, "#############" "# # #" "# $$$$$$$ @#" "#....... #" "#############"

elif BIG == 2

5, 13, "#############" "#... # #" "#.$$$$$$$ @#" "#... #" "#############"

else

11, 19, " ##### " " # # " " # # " " ### #$## " " # # " "### #$## # ######" "# # ## ##### .#" "# $ $ ..#" "##### ### #@## .#" " # #########" " ####### "

endif

);

show_board(s); extend_table(); queue_move(s); for (int i = 0; !done; i++) { printf("depth %d\r", i); fflush(stdout);

state_t *head = next_level; for (next_level = NULL; head && !done; head = head->qnext) do_move(head);

if (!next_level) { puts("no solution?"); return 1; } }

printf("press any key to see moves\n"); getchar(), puts("\033[H\033[J"); show_moves(done);

if 0

free(buckets); free(board); free(goals); free(live);

while (block_root) { void *tmp = block_root->next; free(block_root); block_root = tmp; }

endif

return 0; }</lang>

C++

Set-based Version

Works with: C++11

This heavily abuses the STL, including some of the newer features like regex and tuples.

This performs a breadth-first search by moves, so the results should be a move-optimal solution. <lang cpp>#include <iostream>

include <string>
include <vector>
include <queue>
include <regex>
include <tuple>
include <set>
include <array>

using namespace std;

class Board { public:

 vector<vector<char>> sData, dData;
 int px, py;

 Board(string b)
 {
   regex pattern("([^\\n]+)\\n?");
   sregex_iterator end, iter(b.begin(), b.end(), pattern);
   
   int w = 0;
   vector<string> data;
   for(; iter != end; ++iter){
     data.push_back((*iter)[1]);
     w = max(w, (*iter)[1].length());
   }

   for(int v = 0; v < data.size(); ++v){
     vector<char> sTemp, dTemp;
     for(int u = 0; u < w; ++u){
       if(u > data[v].size()){
         sTemp.push_back(' ');
         dTemp.push_back(' ');
       }else{
         char s = ' ', d = ' ', c = data[v][u];

         if(c == '#')
           s = '#';
         else if(c == '.' || c == '*' || c == '+')
           s = '.';

         if(c == '@' || c == '+'){
           d = '@';
           px = u;
           py = v;
         }else if(c == '$' || c == '*')
           d = '*';

         sTemp.push_back(s);
         dTemp.push_back(d);
       }
     }

     sData.push_back(sTemp);
     dData.push_back(dTemp);
   }
 }

 bool move(int x, int y, int dx, int dy, vector<vector<char>> &data)
 {
   if(sData[y+dy][x+dx] == '#' || data[y+dy][x+dx] != ' ') 
     return false;

   data[y][x] = ' ';
   data[y+dy][x+dx] = '@';

   return true;
 }

 bool push(int x, int y, int dx, int dy, vector<vector<char>> &data)
 {
   if(sData[y+2*dy][x+2*dx] == '#' || data[y+2*dy][x+2*dx] != ' ')
     return false;

   data[y][x] = ' ';
   data[y+dy][x+dx] = '@';
   data[y+2*dy][x+2*dx] = '*';

   return true;
 }

 bool isSolved(const vector<vector<char>> &data)
 {
   for(int v = 0; v < data.size(); ++v)
     for(int u = 0; u < data[v].size(); ++u)
       if((sData[v][u] == '.') ^ (data[v][u] == '*'))
         return false;
   return true;
 }

 string solve()
 {
   set<vector<vector<char>>> visited;
   queue<tuple<vector<vector<char>>, string, int, int>> open;

   open.push(make_tuple(dData, "", px, py));
   visited.insert(dData);

   array<tuple<int, int, char, char>, 4> dirs;
   dirs[0] = make_tuple(0, -1, 'u', 'U');
   dirs[1] = make_tuple(1, 0, 'r', 'R');
   dirs[2] = make_tuple(0, 1, 'd', 'D');
   dirs[3] = make_tuple(-1, 0, 'l', 'L');

   while(open.size() > 0){
     vector<vector<char>> temp, cur = get<0>(open.front());
     string cSol = get<1>(open.front());
     int x = get<2>(open.front());
     int y = get<3>(open.front());
     open.pop();

     for(int i = 0; i < 4; ++i){
       temp = cur;
       int dx = get<0>(dirs[i]);
       int dy = get<1>(dirs[i]);

       if(temp[y+dy][x+dx] == '*'){
         if(push(x, y, dx, dy, temp) && (visited.find(temp) == visited.end())){
           if(isSolved(temp))
             return cSol + get<3>(dirs[i]);
           open.push(make_tuple(temp, cSol + get<3>(dirs[i]), x+dx, y+dy));
           visited.insert(temp);
         }
       }else if(move(x, y, dx, dy, temp) && (visited.find(temp) == visited.end())){
         if(isSolved(temp))
           return cSol + get<2>(dirs[i]);
         open.push(make_tuple(temp, cSol + get<2>(dirs[i]), x+dx, y+dy));
         visited.insert(temp);
       }
     }
   }

   return "No solution";
 }

};

int main() {

 string level =
   "#######\n"
   "#     #\n"
   "#     #\n"
   "#. #  #\n"
   "#. $$ #\n"
   "#.$$  #\n"
   "#.#  @#\n"
   "#######";

 Board b(level);

 cout << level << endl << endl << b.solve() << endl;
 return 0;

}</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

Unordered Set-based Version

Works with: C++11

Works with: Boost

Works with: GCC 4.6

Alternative version, about twice faster (about 2.1 seconds runtime), same output. <lang cpp>#include <iostream>

include <string>
include <vector>
include <queue>
include <tuple>
include <array>
include <map>
include <boost/algorithm/string.hpp>
include <boost/unordered_set.hpp>

using namespace std;

typedef vector<char> TableRow; typedef vector<TableRow> Table;

struct Board {

 Table sData, dData;
 int px, py;

 Board(string b) {
   vector<string> data;
   boost::split(data, b, boost::is_any_of("\n"));

   size_t width = 0;
   for (auto &row: data)
     width = max(width, row.size());

   map<char,char> maps = {{' ',' '}, {'.','.'}, {'@',' '},
                          {'#','#'}, {'$',' '}},
                  mapd = {{' ',' '}, {'.',' '}, {'@','@'},
                          {'#',' '}, {'$','*'}};

   for (size_t r = 0; r < data.size(); r++) {
     TableRow sTemp, dTemp;
     for (size_t c = 0; c < width; c++) {
       char ch = c < data[r].size() ? data[r][c] : ' ';
       sTemp.push_back(maps[ch]);
       dTemp.push_back(mapd[ch]);
       if (ch == '@') {
         px = c;
         py = r;
       }
     }
     sData.push_back(sTemp);
     dData.push_back(dTemp);
   }
 }

 bool move(int x, int y, int dx, int dy, Table &data) {
   if (sData[y+dy][x+dx] == '#' || data[y+dy][x+dx] != ' ')
     return false;

   data[y][x] = ' ';
   data[y+dy][x+dx] = '@';
   return true;
 }

 bool push(int x, int y, int dx, int dy, Table &data) {
   if (sData[y+2*dy][x+2*dx] == '#' || data[y+2*dy][x+2*dx] != ' ')
     return false;

   data[y][x] = ' ';
   data[y+dy][x+dx] = '@';
   data[y+2*dy][x+2*dx] = '*';
   return true;
 }

 bool isSolved(const Table &data) {
   for (size_t r = 0; r < data.size(); r++)
     for (size_t c = 0; c < data[r].size(); c++)
       if ((sData[r][c] == '.') != (data[r][c] == '*'))
         return false;
   return true;
 }

 string solve() {

boost::unordered_set<Table, boost::hash

> visited; visited.insert(dData); queue<tuple<Table, string, int, int>> open; open.push(make_tuple(dData, "", px, py)); vector<tuple<int, int, char, char>> dirs = { make_tuple( 0, -1, 'u', 'U'), make_tuple( 1, 0, 'r', 'R'), make_tuple( 0, 1, 'd', 'D'), make_tuple(-1, 0, 'l', 'L') }; while (open.size() > 0) { Table temp, cur = get<0>(open.front()); string cSol = get<1>(open.front()); int x = get<2>(open.front()); int y = get<3>(open.front()); open.pop(); for (int i = 0; i < 4; ++i) { temp = cur; int dx = get<0>(dirs[i]); int dy = get<1>(dirs[i]); if (temp[y+dy][x+dx] == '*') { if (push(x, y, dx, dy, temp) && visited.find(temp) == visited.end()) { if (isSolved(temp)) return cSol + get<3>(dirs[i]); open.push(make_tuple(temp, cSol + get<3>(dirs[i]), x+dx, y+dy)); visited.insert(temp); } } else if (move(x, y, dx, dy, temp) && visited.find(temp) == visited.end()) { if (isSolved(temp)) return cSol + get<2>(dirs[i]); open.push(make_tuple(temp, cSol + get<2>(dirs[i]), x+dx, y+dy)); visited.insert(temp); } } } return "No solution"; } }; int main() { string level = "#######\n" "# #\n" "# #\n" "#. # #\n" "#. $$ #\n" "#.$$ #\n" "#.# @#\n" "#######"; cout << level << endl << endl; Board board(level); cout << board.solve() << endl; return 0; }</lang>

C#

<lang csharp>using System.Collections.Generic; using System.Linq; using System.Text;

namespace SokobanSolver {

   public class SokobanSolver
   {
       private class Board
       {
           public string Cur { get; internal set; }
           public string Sol { get; internal set; }
           public int X { get; internal set; }
           public int Y { get; internal set; }

           public Board(string cur, string sol, int x, int y)
           {
               Cur = cur;
               Sol = sol;
               X = x;
               Y = y;
           }
       }

       private string destBoard, currBoard;
       private int playerX, playerY, nCols;

       SokobanSolver(string[] board)
       {
           nCols = board[0].Length;
           StringBuilder destBuf = new StringBuilder();
           StringBuilder currBuf = new StringBuilder();

           for (int r = 0; r < board.Length; r++)
           {
               for (int c = 0; c < nCols; c++)
               {

                   char ch = board[r][c];

                   destBuf.Append(ch != '$' && ch != '@' ? ch : ' ');
                   currBuf.Append(ch != '.' ? ch : ' ');

                   if (ch == '@')
                   {
                       this.playerX = c;
                       this.playerY = r;
                   }
               }
           }
           destBoard = destBuf.ToString();
           currBoard = currBuf.ToString();
       }

       private string Move(int x, int y, int dx, int dy, string trialBoard)
       {

           int newPlayerPos = (y + dy) * nCols + x + dx;

           if (trialBoard[newPlayerPos] != ' ')
               return null;

           char[] trial = trialBoard.ToCharArray();
           trial[y * nCols + x] = ' ';
           trial[newPlayerPos] = '@';

           return new string(trial);
       }

       private string Push(int x, int y, int dx, int dy, string trialBoard)
       {

           int newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx;

           if (trialBoard[newBoxPos] != ' ')
               return null;

           char[] trial = trialBoard.ToCharArray();
           trial[y * nCols + x] = ' ';
           trial[(y + dy) * nCols + x + dx] = '@';
           trial[newBoxPos] = '$';

           return new string(trial);
       }

       private bool IsSolved(string trialBoard)
       {
           for (int i = 0; i < trialBoard.Length; i++)
               if ((destBoard[i] == '.')
                       != (trialBoard[i] == '$'))
                   return false;
           return true;
       }

       private string Solve()
       {
           char[,] dirLabels = { { 'u', 'U' }, { 'r', 'R' }, { 'd', 'D' }, { 'l', 'L' } };
           int[,] dirs = { { 0, -1 }, { 1, 0 }, { 0, 1 }, { -1, 0 } };
           ISet<string> history = new HashSet<string>();
           LinkedList<Board> open = new LinkedList<Board>();

           history.Add(currBoard);
           open.AddLast(new Board(currBoard, string.Empty, playerX, playerY));

           while (!open.Count.Equals(0))
           {
               Board item = open.First();
               open.RemoveFirst();
               string cur = item.Cur;
               string sol = item.Sol;
               int x = item.X;
               int y = item.Y;

               for (int i = 0; i < dirs.GetLength(0); i++)
               {
                   string trial = cur;
                   int dx = dirs[i, 0];
                   int dy = dirs[i, 1];

                   // are we standing next to a box ?
                   if (trial[(y + dy) * nCols + x + dx] == '$')
                   {
                       // can we push it ?
                       if ((trial = Push(x, y, dx, dy, trial)) != null)
                       {
                           // or did we already try this one ?
                           if (!history.Contains(trial))
                           {

                               string newSol = sol + dirLabels[i, 1];

                               if (IsSolved(trial))
                                   return newSol;

                               open.AddLast(new Board(trial, newSol, x + dx, y + dy));
                               history.Add(trial);
                           }
                       }
                       // otherwise try changing position
                   }
                   else if ((trial = Move(x, y, dx, dy, trial)) != null)
                   {
                       if (!history.Contains(trial))
                       {
                           string newSol = sol + dirLabels[i, 0];
                           open.AddLast(new Board(trial, newSol, x + dx, y + dy));
                           history.Add(trial);
                       }
                   }
               }
           }
           return "No solution";
       }

       public static void Main(string[] a)
       {
           string level = "#######," +
                          "#     #," +
                          "#     #," +
                          "#. #  #," +
                          "#. $$ #," +
                          "#.$$  #," +
                          "#.#  @#," +
                          "#######";
           System.Console.WriteLine("Level:\n");
           foreach (string line in level.Split(','))
           {
               System.Console.WriteLine(line);
           }
           System.Console.WriteLine("\nSolution:\n");
           System.Console.WriteLine(new SokobanSolver(level.Split(',')).Solve());
       }
   }

}</lang> Output:

Level:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

Solution:

ulULLulDDurrrddlULrruLLrrUruLLLulD

D

Shorter Version

Translation of: C++

This version uses the queue defined in the Queue/Usage task. <lang d>import std.string, std.typecons, std.exception, std.algorithm; import queue_usage2; // No queue in Phobos 2.064.

const struct Board {

   private enum El { floor = ' ', wall = '#', goal = '.',
                     box = '$', player = '@', boxOnGoal='*' }
   private alias CTable = string;
   private immutable size_t ncols;
   private immutable CTable sData, dData;
   private immutable int playerx, playery;

   this(in string[] board) immutable pure nothrow @safe
   in {
       foreach (const row; board) {
           assert(row.length == board[0].length,
                  "Unequal board rows.");
           foreach (immutable c; row)
               assert(c.inPattern(" #.$@*"), "Not valid input");
       }
   } body {
       /*static*/ immutable sMap =
           [' ':' ', '.':'.', '@':' ', '#':'#', '$':' '];
       /*static*/ immutable dMap =
           [' ':' ', '.':' ', '@':'@', '#':' ', '$':'*'];
       ncols = board[0].length;

       int plx = 0, ply = 0;
       CTable sDataBuild, dDataBuild;

       foreach (immutable r, const row; board)
           foreach (immutable c, const ch; row) {
               sDataBuild ~= sMap[ch];
               dDataBuild ~= dMap[ch];
               if (ch == El.player) {
                   plx = c;
                   ply = r;
               }
           }

       this.sData = sDataBuild;
       this.dData = dDataBuild;
       this.playerx = plx;
       this.playery = ply;
   }

   private bool move(in int x, in int y, in int dx,
                     in int dy, ref CTable data)
   const pure nothrow /*@safe*/ {
       if (sData[(y + dy) * ncols + x + dx] == El.wall ||
           data[(y + dy) * ncols + x + dx] != El.floor)
           return false;

       auto data2 = data.dup;
       data2[y * ncols + x] = El.floor;
       data2[(y + dy) * ncols + x + dx] = El.player;
       data = data2.assumeUnique; // Not enforced.
       return true;
   }

   private bool push(in int x, in int y, in int dx,
                     in int dy, ref CTable data)
   const pure nothrow /*@safe*/ {
       if (sData[(y + 2 * dy) * ncols + x + 2 * dx] == El.wall ||
           data[(y + 2 * dy) * ncols + x + 2 * dx] != El.floor)
           return false;

       auto data2 = data.dup;
       data2[y * ncols + x] = El.floor;
       data2[(y + dy) * ncols + x + dx] = El.player;
       data2[(y + 2 * dy) * ncols + x + 2*dx] = El.boxOnGoal;
       data = data2.assumeUnique; // Not enforced.
       return true;
   }

   private bool isSolved(in CTable data)
   const pure nothrow @safe @nogc {
       foreach (immutable i, immutable d; data)
           if ((sData[i] == El.goal) != (d == El.boxOnGoal))
               return false;
       return true;
   }

   string solve() pure nothrow /*@safe*/ {
       bool[immutable CTable] visitedSet = [dData: true];

       alias Four = Tuple!(CTable, string, int, int);
       GrowableCircularQueue!Four open;
       open.push(Four(dData, "", playerx, playery));

       static immutable dirs = [tuple( 0, -1, 'u', 'U'),
                                tuple( 1,  0, 'r', 'R'),
                                tuple( 0,  1, 'd', 'D'),
                                tuple(-1,  0, 'l', 'L')];

       while (!open.empty) {
           //immutable (cur, cSol, x, y) = open.pop;
           immutable item = open.pop;
           immutable cur = item[0];
           immutable cSol = item[1];
           immutable x = item[2];
           immutable y = item[3];

           foreach (immutable di; dirs) {
               CTable temp = cur;
               //immutable (dx, dy) = di[0 .. 2];
               immutable dx = di[0];
               immutable dy = di[1];

               if (temp[(y + dy) * ncols + x + dx] == El.boxOnGoal) {
                   if (push(x, y, dx, dy, temp) && temp !in visitedSet) {
                       if (isSolved(temp))
                           return cSol ~ di[3];
                       open.push(Four(temp, cSol ~ di[3], x + dx, y + dy));
                       visitedSet[temp] = true;
                   }
               } else if (move(x, y, dx, dy, temp) && temp !in visitedSet) {
                   if (isSolved(temp))
                       return cSol ~ di[2];
                   open.push(Four(temp, cSol ~ di[2], x + dx, y + dy));
                   visitedSet[temp] = true;
               }
           }
       }

       return "No solution";
   }

}

void main() {

   import std.stdio, core.memory;
   GC.disable; // Uses about twice the memory.

   immutable level =

"#######

#
#
. # #
. $$ #
.$$ #
.# @#
1. 1. 1. 1. ";

   immutable b = immutable(Board)(level.splitLines);
   writeln(level, "\n\n", b.solve);

}</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

Run-time about 0.55 seconds with DMD compiler, 0.49 with LDC2 compiler.

Faster Version

Translation of: C

This code is not idiomatic D, it retains most of the style of the C version. <lang d>import core.stdc.stdio: printf, puts, fflush, stdout, putchar; import core.stdc.stdlib: malloc, calloc, realloc, free, alloca, exit;

enum Cell : ubyte { space, wall, player, box } alias CellIndex = ushort; alias Thash = uint;

/// Board configuration is represented by an array of cell /// indices of player and boxes. struct State { // Variable length struct.

   Thash h;
   State* prev, next, qNext;
   CellIndex[0] c_;

   CellIndex get(in size_t i) inout pure nothrow @nogc {
       return c_.ptr[i];
   }

   void set(in size_t i, in CellIndex v) pure nothrow @nogc {
       c_.ptr[i] = v;
   }

   CellIndex[] slice(in size_t i, in size_t j) pure nothrow @nogc return {
       return c_.ptr[i .. j];
   }

}

__gshared Cell[] board; __gshared bool[] goals, live; __gshared size_t w, h, nBoxes, stateSize, blockSize = 32; __gshared State* blockRoot, blockHead, nextLevel, done; __gshared State*[] buckets; __gshared Thash hashSize, fillLimit, filled;

State* newState(State* parent) nothrow @nogc {

   static State* nextOf(State *s) nothrow @nogc {
       return cast(State*)(cast(ubyte*)s + stateSize);
   }

   State* ptr;
   if (!blockHead) {
       blockSize *= 2;
       auto p = cast(State*)malloc(blockSize * stateSize);
       if (p == null)
           exit(1);

       p.next = blockRoot;
       blockRoot = p;
       ptr = cast(State*)(cast(ubyte*)p + stateSize * blockSize);
       p = blockHead = nextOf(p);
       for (auto q = nextOf(p); q < ptr; p = q, q = nextOf(q))
           p.next = q;
       p.next = null;
   }

   ptr = blockHead;
   blockHead = blockHead.next;
   ptr.prev = parent;
   ptr.h = 0;
   return ptr;

}

void unNewState(State* p) nothrow @nogc {

   p.next = blockHead;
   blockHead = p;

}

/// Mark up positions where a box definitely should not be. void markLive(in size_t c) nothrow @nogc {

   immutable y = c / w;
   immutable x = c % w;
   if (live[c])
       return;

   live[c] = true;
   if (y > 1 && board[c - w] != Cell.wall &&
       board[c - w * 2] != Cell.wall)
       markLive(c - w);
   if (y < h - 2 && board[c + w] != Cell.wall &&
       board[c + w * 2] != Cell.wall)
       markLive(c + w);
   if (x > 1 && board[c - 1] != Cell.wall &&
       board[c - 2] != Cell.wall)
       markLive(c - 1);
   if (x < w - 2 && board[c + 1] != Cell.wall &&
       board[c + 2] != Cell.wall)
       markLive(c + 1);

}

State* parseBoard(in size_t y, in size_t x, in char* s) nothrow @nogc {

   static T[] myCalloc(T)(in size_t n) nothrow @nogc {
       auto ptr = cast(T*)calloc(n, T.sizeof);
       if (ptr == null)
           exit(1);
       return ptr[0 .. n];
   }

   w = x, h = y;
   board = myCalloc!Cell(w * h);
   goals = myCalloc!bool(w * h);
   live = myCalloc!bool(w * h);

   nBoxes = 0;
   for (int i = 0; s[i]; i++) {
       switch(s[i]) {
           case '#':
               board[i] = Cell.wall;
               continue;
           case '.', '+':
               goals[i] = true;
               goto case;
           case '@':
               continue;
           case '*':
               goals[i] = true;
               goto case;
           case '$':
               nBoxes++;
               continue;
           default:
               continue;
       }
   }

   enum int intSize = int.sizeof;
   stateSize = (State.sizeof +
                 (1 + nBoxes) * CellIndex.sizeof +
                 intSize - 1)
                / intSize * intSize;

   auto state = null.newState;

   for (CellIndex i = 0, j = 0; i < w * h; i++) {
       if (goals[i])
           i.markLive;
       if (s[i] == '$' || s[i] == '*')
           state.set(++j, i);
       else if (s[i] == '@' || s[i] == '+')
           state.set(0, i);
   }

   return state;

}

/// K&R hash function. void hash(State* s, in size_t nBoxes) pure nothrow @nogc {

   if (!s.h) {
       Thash ha = 0;
       foreach (immutable i; 0 .. nBoxes + 1)
           ha = s.get(i) + 31 * ha;
       s.h = ha;
   }

}

void extendTable() nothrow @nogc {

   int oldSize = hashSize;

   if (!oldSize) {
       hashSize = 1024;
       filled = 0;
       fillLimit = hashSize * 3 / 4; // 0.75 load factor.
   } else {
       hashSize *= 2;
       fillLimit *= 2;
   }

   auto ptr = cast(State**)realloc(buckets.ptr,
                                   (State*).sizeof * hashSize);
   if (ptr == null)
       exit(6);
   buckets = ptr[0 .. hashSize];
   buckets[oldSize .. hashSize] = null;

   immutable Thash bits = hashSize - 1;
   foreach (immutable i; 0 .. oldSize) {
       auto head = buckets[i];
       buckets[i] = null;
       while (head) {
           auto next = head.next;
           immutable j = head.h & bits;
           head.next = buckets[j];
           buckets[j] = head;
           head = next;
       }
   }

}

State* lookup(State *s) nothrow @nogc {

   s.hash(nBoxes);
   auto f = buckets[s.h & (hashSize - 1)];
   for (; f; f = f.next) {
       if (s.slice(0, nBoxes + 1) == f.slice(0, nBoxes + 1))
           break;
   }

   return f;

}

bool addToTable(State* s) nothrow @nogc {

   if (s.lookup) {
       s.unNewState;
       return false;
   }

   if (filled++ >= fillLimit)
       extendTable;

   immutable Thash i = s.h & (hashSize - 1);

   s.next = buckets[i];
   buckets[i] = s;
   return true;

}

bool success(in State* s) nothrow @nogc {

   foreach (immutable i; 1 .. nBoxes + 1)
       if (!goals[s.get(i)])
           return false;
   return true;

}

State* moveMe(State* s, in int dy, in int dx) nothrow @nogc {

   immutable int y = s.get(0) / w;
   immutable int x = s.get(0) % w;
   immutable int y1 = y + dy;
   immutable int x1 = x + dx;
   immutable int c1 = y1 * w + x1;

   if (y1 < 0 || y1 > h || x1 < 0 || x1 > w || board[c1] == Cell.wall)
       return null;

   int atBox = 0;
   foreach (immutable i; 1 .. nBoxes + 1)
       if (s.get(i) == c1) {
           atBox = i;
           break;
       }

   int c2;
   if (atBox) {
       c2 = c1 + dy * w + dx;
       if (board[c2] == Cell.wall || !live[c2])
           return null;
       foreach (immutable i; 1 .. nBoxes + 1)
           if (s.get(i) == c2)
               return null;
   }

   auto n = s.newState;
   n.slice(1, nBoxes + 1)[] = s.slice(1, nBoxes + 1);

   n.set(0, cast(CellIndex)c1);

   if (atBox)
       n.set(atBox, cast(CellIndex)c2);

   // Bubble sort.
   for (size_t i = nBoxes; --i; ) {
       CellIndex t = 0;
       foreach (immutable j; 1 .. i) {
           if (n.get(j) > n.get(j + 1)) {
               t = n.get(j);
               n.set(j, n.get(j + 1));
               n.set(j + 1, t);
           }
       }
       if (!t)
           break;
   }

   return n;

}

bool queueMove(State *s) nothrow @nogc {

   if (!s || !s.addToTable)
       return false;

   if (s.success) {
       "\nSuccess!".puts;
       done = s;
       return true;
   }

   s.qNext = nextLevel;
   nextLevel = s;
   return false;

}

bool doMove(State* s) nothrow @nogc {

   return s.moveMe( 1,  0).queueMove ||
          s.moveMe(-1,  0).queueMove ||
          s.moveMe( 0,  1).queueMove ||
          s.moveMe( 0, -1).queueMove;

}

void showBoard(in State* s) nothrow @nogc {

   static immutable glyphs1 = " #@$", glyphs2 = ".#@$";

   auto ptr = cast(ubyte*)alloca(w * h * ubyte.sizeof);
   if (ptr == null)
       exit(5);
   auto b = ptr[0 .. w * h];
   b[] = cast(typeof(b))board[];

   b[s.get(0)] = Cell.player;
   foreach (immutable i; 1 .. nBoxes + 1)
       b[s.get(i)] = Cell.box;

   foreach (immutable i, immutable bi; b) {
       putchar((goals[i] ? glyphs2 : glyphs1)[bi]);
       if (!((1 + i) % w))
           '\n'.putchar;
   }

}

void showMoves(in State* s) nothrow @nogc {

   if (s.prev)
       s.prev.showMoves;
   "\n".printf;
   s.showBoard;

}

int main() nothrow @nogc {

   // Workaround for @nogc.
   alias ctEval(alias expr) = expr;

   enum uint problem = 0;

   static if (problem == 0) {
       auto s = parseBoard(8, 7, ctEval!(
       "#######"~
       "#     #"~
       "#     #"~
       "#. #  #"~
       "#. $$ #"~
       "#.$$  #"~
       "#.#  @#"~
       "#######"));

   } else static if (problem == 1) {
       auto s = parseBoard(5, 13, ctEval!(
       "#############"~
       "#  #        #"~
       "# $$$$$$$  @#"~
       "#.......    #"
       "#############"));

   } else static if (problem == 2) {
       auto s = parseBoard(11, 19, ctEval!(
       "    #####          "~
       "    #   #          "~
       "    #   #          "~
       "  ### #$##         "~
       "  #      #         "~
       "### #$## #   ######"~
       "#   # ## #####   .#"~
       "# $   $         ..#"~
       "##### ### #@##   .#"~
       "    #     #########"~
       "    #######        "));
   } else {
       asset(0, "Not present problem.");
   }

   s.showBoard;
   extendTable;
   s.queueMove;
   for (int i = 0; !done; i++) {
       printf("depth %d\r", i);
       stdout.fflush;

       auto head = nextLevel;
       for (nextLevel = null; head && !done; head = head.qNext)
           head.doMove;

       if (!nextLevel) {
           "No solution?".puts;
           return 1;
       }
   }

   done.showMoves;

   version (none) { // Free all allocated memory.
       buckets.ptr.free;
       board.ptr.free;
       goals.ptr.free;
       live.ptr.free;

       while (blockRoot) {
           auto tmp = blockRoot.next;
           blockRoot.free;
           blockRoot = tmp;
       }
   }

   return 0;

}</lang>

Elixir

Works with: Elixir version 1.3

Translation of: Ruby

<lang elixir>defmodule Sokoban do

 defp setup(level) do
   {leng, board} = normalize(level)
   {player, goal} = check_position(board)
   board = replace(board, [{".", " "}, {"+", " "}, {"*", "$"}])
   lurd = [{-1, "l", "L"}, {-leng, "u", "U"}, {1, "r", "R"}, {leng, "d", "D"}]
   dirs = [-1, -leng, 1, leng]
   dead_zone = set_dead_zone(board, goal, dirs)
   {board, player, goal, lurd, dead_zone}
 end
 
 defp normalize(level) do
   board = String.split(level, "\n", trim: true)
           |> Enum.map(&String.trim_trailing &1)
   leng  = Enum.map(board, &String.length &1) |> Enum.max
   board = Enum.map(board, &String.pad_trailing(&1, leng)) |> Enum.join
   {leng, board}
 end
 
 defp check_position(board) do
   board = String.codepoints(board)
   player = Enum.find_index(board, fn c -> c in ["@", "+"] end)
   goal = Enum.with_index(board)
          |> Enum.filter_map(fn {c,_} -> c in [".", "+", "*"] end, fn {_,i} -> i end)
   {player, goal}
 end
 
 defp set_dead_zone(board, goal, dirs) do
   wall = String.replace(board, ~r/[^#]/, " ")
          |> String.codepoints
          |> Enum.with_index
          |> Enum.into(Map.new, fn {c,i} -> {i,c} end)
   corner = search_corner(wall, goal, dirs)
   set_dead_zone(wall, dirs, goal, corner, corner)
 end
 
 defp set_dead_zone(wall, dirs, goal, corner, dead) do
   dead2 = Enum.reduce(corner, dead, fn pos,acc ->
             Enum.reduce(dirs, acc, fn dir,acc2 ->
               if wall[pos+dir] == "#", do: acc2,
                   else: acc2 ++ check_side(wall, dirs, pos+dir, dir, goal, dead, [])
             end)
           end)
   if dead == dead2, do: :lists.usort(dead),
                   else: set_dead_zone(wall, dirs, goal, corner, dead2)
 end
 
 defp replace(string, replacement) do
   Enum.reduce(replacement, string, fn {a,b},str ->
     String.replace(str, a, b)
   end)
 end
 
 defp search_corner(wall, goal, dirs) do
   Enum.reduce(wall, [], fn {i,c},corner ->
     if c == "#" or i in goal do
       corner
     else
       case count_wall(wall, i, dirs) do
         2 -> if wall[i-1] != wall[i+1], do: [i | corner], else: corner
         3 -> [i | corner]
         _ -> corner
       end
     end
   end)
 end
 
 defp check_side(wall, dirs, pos, dir, goal, dead, acc) do
   if wall[pos] == "#" or
     count_wall(wall, pos, dirs) == 0 or
     pos in goal do
     []
   else
     if pos in dead, do: acc, else: check_side(wall, dirs, pos+dir, dir, goal, dead, [pos|acc])
   end
 end
 
 defp count_wall(wall, pos, dirs) do
   Enum.count(dirs, fn dir -> wall[pos + dir] == "#" end)
 end
 
 defp push_box(board, pos, dir, route, goal, dead_zone) do
   pos2dir = pos + 2 * dir
   if String.at(board, pos2dir) == " " and not pos2dir in dead_zone do
     board2 = board |> replace_at(pos,     " ")
                    |> replace_at(pos+dir, "@")
                    |> replace_at(pos2dir, "$")
     unless visited?(board2) do
       if solved?(board2, goal) do
         IO.puts route
         exit(:normal)
       else
         queue_in({board2, pos+dir, route})
       end
     end
   end
 end
 
 defp move_player(board, pos, dir) do
   board |> replace_at(pos, " ") |> replace_at(pos+dir, "@")
 end
 
 defp replace_at(str, pos, c) do
   {left, right} = String.split_at(str, pos)
   {_, right} = String.split_at(right, 1)
   left <> c <> right
   # String.slice(str, 0, pos) <> c <> String.slice(str, pos+1..-1)
 end
 
 defp solved?(board, goal) do
   Enum.all?(goal, fn g -> String.at(board, g) == "$" end)
 end
 
 @pattern :sokoban_pattern_set
 @queue   :sokoban_queue
 
 defp start_link do
   Agent.start_link(fn -> MapSet.new end, name: @pattern)
   Agent.start_link(fn -> :queue.new end, name: @queue)
 end
 
 defp visited?(board) do
   Agent.get_and_update(@pattern, fn set ->
     {board in set, MapSet.put(set, board)}
   end)
 end
 
 defp queue_in(data) do
   Agent.update(@queue, fn queue -> :queue.in(data, queue) end)
 end
 
 defp queue_out do
   Agent.get_and_update(@queue, fn q ->
     case :queue.out(q) do
       {{:value, data}, queue} -> {data, queue}
       x -> x
     end
   end)
 end
 
 def solve(level) do
   {board, player, goal, lurd, dead_zone} = setup(level)
   start_link
   visited?(board)
   queue_in({board, player, ""})
   solve(goal, lurd, dead_zone)
 end
 
 defp solve(goal, lurd, dead_zone) do
   case queue_out do
     {board, pos, route} ->
       Enum.each(lurd, fn {dir,move,push} ->
         case String.at(board, pos+dir) do
           "$" -> push_box(board, pos, dir, route<>push, goal, dead_zone)
           " " -> board2 = move_player(board, pos, dir)
                  unless visited?(board2) do
                    queue_in({board2, pos+dir, route<>move})
                  end
           _ -> :not_move    # wall
         end
       end)
     _ ->
       IO.puts "No solution"
       exit(:normal)
   end
   solve(goal, lurd, dead_zone)
 end

end

level = """

#
#
. # #
. $$ #
.$$ #
.# @#

""" IO.puts level Sokoban.solve(level)</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

luULLulDDurrrddlULrruLLrrUruLLLulD

Go

Translation of: C++

Well, it started as a C++ translation, but turned out different. It's still the breadth-first set-based algorithm, but I dropped the sdata/ddata optimization and just maintained a single string as the board representation. Also dropped the code to handle non-rectangular boards, and probably some other stuff too. <lang go>package main

import (

   "fmt"
   "strings"

)

func main() {

   level := `

#
#
. # #
. $$ #
.$$ #
.# @#
1. 1. 1. 1. `

   fmt.Printf("level:%s\n", level)
   fmt.Printf("solution:\n%s\n", solve(level))

}

func solve(board string) string {

   buffer = make([]byte, len(board))
   width := strings.Index(board[1:], "\n") + 1
   dirs := []struct {
       move, push string 
       dPos       int
   }{
       {"u", "U", -width},
       {"r", "R", 1},
       {"d", "D", width},
       {"l", "L", -1},
   }
   visited := map[string]bool{board: true}
   open := []state{state{board, "", strings.Index(board, "@")}}
   for len(open) > 0 {
       s1 := &open[0]
       open = open[1:]
       for _, dir := range dirs {
           var newBoard, newSol string
           newPos := s1.pos + dir.dPos
           switch s1.board[newPos] {
           case '$', '*':
               newBoard = s1.push(dir.dPos)
               if newBoard == "" || visited[newBoard] {
                   continue
               }
               newSol = s1.cSol + dir.push
               if strings.IndexAny(newBoard, ".+") < 0 {
                   return newSol
               }
           case ' ', '.':
               newBoard = s1.move(dir.dPos)
               if visited[newBoard] {
                   continue
               }
               newSol = s1.cSol + dir.move
           default:
               continue
           }
           open = append(open, state{newBoard, newSol, newPos})
           visited[newBoard] = true
       }
   }
   return "No solution"

}

type state struct {

   board string
   cSol  string
   pos   int

}

var buffer []byte

func (s *state) move(dPos int) string {

   copy(buffer, s.board)
   if buffer[s.pos] == '@' {
       buffer[s.pos] = ' '
   } else {
       buffer[s.pos] = '.'
   }
   newPos := s.pos + dPos
   if buffer[newPos] == ' ' {
       buffer[newPos] = '@'
   } else {
       buffer[newPos] = '+'
   }
   return string(buffer)

}

func (s *state) push(dPos int) string {

   newPos := s.pos + dPos
   boxPos := newPos + dPos
   switch s.board[boxPos] {
   case ' ', '.':
   default:
       return ""
   }
   copy(buffer, s.board)
   if buffer[s.pos] == '@' {
       buffer[s.pos] = ' '
   } else {
       buffer[s.pos] = '.'
   }
   if buffer[newPos] == '$' {
       buffer[newPos] = '@'
   } else {
       buffer[newPos] = '+'
   }
   if buffer[boxPos] == ' ' {
       buffer[boxPos] = '$'
   } else {
       buffer[boxPos] = '*'
   }
   return string(buffer)

}</lang>

Output:

level:
#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######
solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD

Haskell

<lang Haskell>import Control.Monad (liftM) import Data.Array import Data.List (transpose) import Data.Maybe (mapMaybe) import qualified Data.Sequence as Seq import qualified Data.Set as Set import Prelude hiding (Left, Right)

data Field = Space | Wall | Goal

          deriving (Eq)

instance Show Action where

 show Up        = "u"
 show Down      = "d"
 show Left      = "l"
 show Right     = "r"
 show PushUp    = "U"
 show PushDown  = "D"
 show PushLeft  = "L"
 show PushRight = "R"

type Index = (Int, Int) type FieldArray = Array Index Field type BoxArray = Array Index Bool type PlayerPos = Index type GameState = (BoxArray, PlayerPos) type Game = (FieldArray, GameState)

toField :: Char -> Field toField '#' = Wall toField ' ' = Space toField '@' = Space toField '$' = Space toField '.' = Goal toField '+' = Goal toField '*' = Goal

toPush :: Action -> Action toPush Up = PushUp toPush Down = PushDown toPush Left = PushLeft toPush Right = PushRight toPush n = n

toMove :: Action -> Index toMove PushUp = ( 0, -1) toMove PushDown = ( 0, 1) toMove PushLeft = (-1, 0) toMove PushRight = ( 1, 0) toMove n = toMove $ toPush n

-- Parse the string-based game board into an easier-to-use format. -- Assume that the board is valid (rectangular, one player, etc). parseGame :: [String] -> Game parseGame fieldStrs = (field, (boxes, player))

 where
   width     = length $ head fieldStrs
   height    = length fieldStrs
   bound     = ((0, 0), (width - 1, height - 1))
   flatField = concat $ transpose fieldStrs
   charField = listArray bound flatField
   field     = fmap toField charField
   boxes     = fmap (`elem` "$*") charField
   player    = fst $ head $ filter (flip elem "@+" . snd) $ assocs charField

add :: (Num a, Num b) => (a, b) -> (a, b) -> (a, b) add (a, b) (x, y) = (a + x, b + y)

-- Attempt to perform an action, returning the updated game and adjusted -- action if the action was legal. tryAction :: Game -> Action -> Maybe (Game, Action) tryAction (field, (boxes, player)) action

 | field ! vec == Wall = Nothing
 | boxes ! vec =
    if boxes ! vecB || field ! vecB == Wall
    then Nothing
    else Just ((field, (boxes // [(vec, False), (vecB, True)], vec)),
              toPush action)
 | otherwise = Just ((field, (boxes, vec)), action)
 where
   actionVec = toMove action
   vec       = player `add` actionVec
   vecB      = vec `add` actionVec

-- Search the game for a solution. solveGame :: Game -> Maybe [Action] solveGame (field, initState) =

 liftM reverse $ bfs (Seq.singleton (initState, [])) (Set.singleton initState)
 where
   goals           = map fst $ filter ((== Goal) . snd) $ assocs field
   isSolved st     = all (st !) goals
   possibleActions = [Up, Down, Left, Right]
   
   -- Breadth First Search of the game tree.
   bfs :: Seq.Seq (GameState, [Action]) -> Set.Set GameState -> Maybe [Action]
   bfs queue visited =
     case Seq.viewl queue of
       Seq.EmptyL -> Nothing
       (game@(boxes, _), actions) Seq.:< queueB ->
         if isSolved boxes
         then Just actions
         else
           let newMoves = filter (flip Set.notMember visited . fst) $
                          map (\((_, g), a) -> (g, a)) $
                          mapMaybe (tryAction (field, game)) possibleActions
               visitedB = foldl (flip Set.insert) visited $
                          map fst newMoves
               queueC   = foldl (Seq.|>) queueB $
                          map (\(g, a) -> (g, a:actions)) newMoves
           in bfs queueC visitedB

exampleA :: [String] exampleA =

 ["#######"
 ,"#     #"
 ,"#     #"
 ,"#. #  #"
 ,"#. $$ #"
 ,"#.$$  #"
 ,"#.#  @#"
 ,"#######"]

main :: IO () main =

 case solveGame $ parseGame exampleA of
   Nothing       -> putStrLn "Unsolvable"
   Just solution -> do
     mapM_ putStrLn exampleA
     putStrLn ""
     putStrLn $ concatMap show solution</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

Java

Translation of C++ via D

Works with: Java version 7

<lang java>import java.util.*;

public class Sokoban {

   String destBoard, currBoard;
   int playerX, playerY, nCols;

   Sokoban(String[] board) {
       nCols = board[0].length();
       StringBuilder destBuf = new StringBuilder();
       StringBuilder currBuf = new StringBuilder();

       for (int r = 0; r < board.length; r++) {
           for (int c = 0; c < nCols; c++) {

               char ch = board[r].charAt(c);

               destBuf.append(ch != '$' && ch != '@' ? ch : ' ');
               currBuf.append(ch != '.' ? ch : ' ');

               if (ch == '@') {
                   this.playerX = c;
                   this.playerY = r;
               }
           }
       }
       destBoard = destBuf.toString();
       currBoard = currBuf.toString();
   }

   String move(int x, int y, int dx, int dy, String trialBoard) {

       int newPlayerPos = (y + dy) * nCols + x + dx;

       if (trialBoard.charAt(newPlayerPos) != ' ')
           return null;

       char[] trial = trialBoard.toCharArray();
       trial[y * nCols + x] = ' ';
       trial[newPlayerPos] = '@';

       return new String(trial);
   }

   String push(int x, int y, int dx, int dy, String trialBoard) {

       int newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx;

       if (trialBoard.charAt(newBoxPos) != ' ')
           return null;

       char[] trial = trialBoard.toCharArray();
       trial[y * nCols + x] = ' ';
       trial[(y + dy) * nCols + x + dx] = '@';
       trial[newBoxPos] = '$';

       return new String(trial);
   }

   boolean isSolved(String trialBoard) {
       for (int i = 0; i < trialBoard.length(); i++)
           if ((destBoard.charAt(i) == '.')
                   != (trialBoard.charAt(i) == '$'))
               return false;
       return true;
   }

   String solve() {
       class Board {
           String cur, sol;
           int x, y;

           Board(String s1, String s2, int px, int py) {
               cur = s1;
               sol = s2;
               x = px;
               y = py;
           }
       }
       char[][] dirLabels = {{'u', 'U'}, {'r', 'R'}, {'d', 'D'}, {'l', 'L'}};
       int[][] dirs = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}};

       Set<String> history = new HashSet<>();
       LinkedList<Board> open = new LinkedList<>();

       history.add(currBoard);
       open.add(new Board(currBoard, "", playerX, playerY));

       while (!open.isEmpty()) {
           Board item = open.poll();
           String cur = item.cur;
           String sol = item.sol;
           int x = item.x;
           int y = item.y;

           for (int i = 0; i < dirs.length; i++) {
               String trial = cur;
               int dx = dirs[i][0];
               int dy = dirs[i][1];

               // are we standing next to a box ?
               if (trial.charAt((y + dy) * nCols + x + dx) == '$') {

                   // can we push it ?
                   if ((trial = push(x, y, dx, dy, trial)) != null) {

                       // or did we already try this one ?
                       if (!history.contains(trial)) {

                           String newSol = sol + dirLabels[i][1];

                           if (isSolved(trial))
                               return newSol;

                           open.add(new Board(trial, newSol, x + dx, y + dy));
                           history.add(trial);
                       }
                   }

               // otherwise try changing position
               } else if ((trial = move(x, y, dx, dy, trial)) != null) {

                   if (!history.contains(trial)) {
                       String newSol = sol + dirLabels[i][0];
                       open.add(new Board(trial, newSol, x + dx, y + dy));
                       history.add(trial);
                   }
               }
           }
       }
       return "No solution";
   }

   public static void main(String[] a) {
       String level = "#######,#     #,#     #,#. #  #,#. $$ #,"
               + "#.$$  #,#.#  @#,#######";
       System.out.println(new Sokoban(level.split(",")).solve());
   }

}</lang>

ulULLulDDurrrddlULrruLLrrUruLLLulD

Julia

Translation of: Go

<lang julia>struct BoardState

   board::String
   csol::String
   position::Int

end

function move(s::BoardState, dpos)

   buffer = Vector{UInt8}(deepcopy(s.board))
   if s.board[s.position] == '@'
       buffer[s.position] = ' '
   else
       buffer[s.position] = '.'
   end
   newpos = s.position + dpos
   if s.board[newpos] == ' '
       buffer[newpos] = '@'
   else
       buffer[newpos] = '+'
   end
   String(buffer)

end

function push(s::BoardState, dpos)

   newpos = s.position + dpos
   boxpos = newpos + dpos
   if s.board[boxpos] != ' ' && s.board[boxpos] != '.'
       return ""
   end
   buffer = Vector{UInt8}(deepcopy(s.board))
   if s.board[s.position] == '@'
       buffer[s.position] = ' '
   else
       buffer[s.position] = '.'
   end
   if s.board[newpos] == '$'
       buffer[newpos] = '@'
   else
       buffer[newpos] = '+'
   end
   if s.board[boxpos] == ' '
       buffer[boxpos] = '$'
   else
       buffer[boxpos] = '*'
   end
   String(buffer)

end

function solve(board)

   width = findfirst("\n", board[2:end])[1] + 1
   dopt = (u = -width, l = -1, d = width, r = 1)
   visited = Dict(board => true)
   open::Vector{BoardState} = [BoardState(board, "", findfirst("@", board)[1])]
   while length(open) > 0
       s1 = open[1]
       open = open[2:end]
       for dir in keys(dopt)
           newpos = s1.position + dopt[dir]
           x = s1.board[newpos]
           if x == '$' || x == '*'
               newboard = push(s1, dopt[dir])
               if newboard == "" || haskey(visited, newboard)
                   continue
               end
               newsol = s1.csol * uppercase(string(dir))
               if findfirst(r"[\.\+]", newboard) ==  nothing
                   return newsol
               end
           elseif x == ' ' || x == '.'
               newboard = move(s1, dopt[dir])
               if haskey(visited, newboard)
                   continue
               end
               newsol = s1.csol * string(dir)
           else
               continue
           end
           open = push!(open, BoardState(newboard, newsol, newpos))
           visited[newboard] = true
       end
   end
   "No solution" # we should only get here if no solution to the sokoban

end

const testlevel = strip(raw"""

#
#
. # #
. $$ #
.$$ #
.# @#
1. 1. 1. 1. """)

println("For sokoban level:\n$testlevel\n...solution is :\n$(solve(testlevel))")

</lang>

Output:


For sokoban level:
#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######
...solution is :
ulULLulDDurrrddlULrruLrUruLLLulD

Kotlin

Translation of: Java

<lang scala>// version 1.2.0

import java.util.LinkedList

class Sokoban(board: List<String>) {

   val destBoard: String
   val currBoard: String
   val nCols = board[0].length
   var playerX = 0
   var playerY = 0

   init {
       val destBuf = StringBuilder()
       val currBuf = StringBuilder()
       for (r in 0 until board.size) {
           for (c in 0 until nCols) {
               val ch = board[r][c]
               destBuf.append(if (ch != '$' && ch != '@') ch else ' ')
               currBuf.append(if (ch != '.') ch else ' ')
               if (ch == '@') {
                   playerX = c
                   playerY = r
               }
           }
       }
       destBoard = destBuf.toString()
       currBoard = currBuf.toString()
   }

   fun move(x: Int, y: Int, dx: Int, dy: Int, trialBoard: String): String {
       val newPlayerPos = (y + dy) * nCols + x + dx
       if (trialBoard[newPlayerPos] != ' ') return ""
       val trial = trialBoard.toCharArray()
       trial[y * nCols + x] = ' '
       trial[newPlayerPos] = '@'
       return String(trial)
   }

   fun push(x: Int, y: Int, dx: Int, dy: Int, trialBoard: String): String {
       val newBoxPos = (y + 2 * dy) * nCols + x + 2 * dx
       if (trialBoard[newBoxPos] != ' ') return ""
       val trial = trialBoard.toCharArray()
       trial[y * nCols + x] = ' '
       trial[(y + dy) * nCols + x + dx] = '@'
       trial[newBoxPos] = '$'
       return String(trial)
   }

   fun isSolved(trialBoard: String): Boolean {
       for (i in 0 until trialBoard.length) {
           if ((destBoard[i] == '.') != (trialBoard[i] == '$')) return false
       }
       return true
   }

   fun solve(): String {
       data class Board(val cur: String, val sol: String, val x: Int, val y: Int)
       val dirLabels = listOf('u' to 'U', 'r' to 'R', 'd' to 'D', 'l' to 'L')
       val dirs = listOf(0 to -1, 1 to 0, 0 to 1, -1 to 0)
       val history = mutableSetOf<String>()
       history.add(currBoard)
       val open = LinkedList<Board>()
       open.add(Board(currBoard, "", playerX, playerY))

       while (!open.isEmpty()) {
           val (cur, sol, x, y) = open.poll()
           for (i in 0 until dirs.size) {
               var trial = cur
               val dx = dirs[i].first
               val dy = dirs[i].second

               // are we standing next to a box ?
               if (trial[(y + dy) * nCols + x + dx] == '$') {

                   // can we push it ?
                   trial = push(x, y, dx, dy, trial)
                   if (!trial.isEmpty()) {

                       // or did we already try this one ?
                       if (trial !in history) {
                           val newSol = sol + dirLabels[i].second
                           if (isSolved(trial)) return newSol
                           open.add(Board(trial, newSol, x + dx, y + dy))
                           history.add(trial)
                       }
                   }
               } // otherwise try changing position
               else {
                   trial = move(x, y, dx, dy, trial)
                   if (!trial.isEmpty() && trial !in history) {
                       val newSol = sol + dirLabels[i].first
                       open.add(Board(trial, newSol, x + dx, y + dy))
                       history.add(trial)
                   }
               }
           }          
       }
       return "No solution"
   }

}

fun main(args: Array<String>) {

   val level = listOf(
       "#######",
       "#     #",
       "#     #",
       "#. #  #",
       "#. $$ #",
       "#.$$  #",
       "#.#  @#",
       "#######"
   )
   println(level.joinToString("\n"))
   println()
   println(Sokoban(level).solve())

}</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

OCaml

Translation of: Python

This uses a breadth-first move search, so will find a move-optimal solution. <lang OCaml>type dir = U | D | L | R type move_t = Move of dir | Push of dir

let letter = function

  | Push(U) -> 'U' | Push(D) -> 'D' | Push(L) -> 'L' | Push(R) -> 'R'
  | Move(U) -> 'u' | Move(D) -> 'd' | Move(L) -> 'l' | Move(R) -> 'r'

let cols = ref 0 let delta = function U -> -(!cols) | D -> !cols | L -> -1 | R -> 1

let store = Hashtbl.create 251 let mark t = Hashtbl.replace store t () let marked t = Hashtbl.mem store t

let show ml =

  List.iter (fun c -> print_char (letter c)) (List.rev ml); print_newline()

let gen_moves (x,boxes) bd =

  let empty i = bd.(i) = ' ' && not (List.mem i boxes) in
  let check l dir =
     let dx = delta dir in
     let x1 = x+dx in
     if List.mem x1 boxes then (
        if empty (x1+dx) then Push(dir) :: l else l
     ) else (
        if bd.(x1) = ' ' then Move(dir) :: l else l
     ) in
  (List.fold_left check [] [U; L; R; D])

let do_move (x,boxes) = function

  | Push(d) -> let dx = delta d in
     let x1 = x+dx in let x2 = x1+dx in
     let rec shift = function
        | [] -> failwith "shift"
        | h :: t -> if h = x1 then x2 :: t else h :: shift t in
     x1, List.fast_sort compare (shift boxes)
  | Move(d) -> (x+(delta d)), boxes

let init_pos bd =

  let p = ref 0 in
  let q = ref [] in 
  let check i c =
     if c = '$' || c = '*' then q := i::!q
     else if c = '@' then p := i in (
  Array.iteri check bd;
  (!p, List.fast_sort compare !q);
  )

let final_box bd =

  let check (i,l) c = if c = '.' || c = '*' then (i+1,i::l) else (i+1,l) in
  List.fast_sort compare (snd (Array.fold_left check (0,[]) bd))

let array_of_input inp =

  let r = List.length inp and c = String.length (List.hd inp) in
  let a = Array.create (r*c) ' ' in (
  for i = 0 to pred r do
     let s = List.nth inp i in
     for j = 0 to pred c do a.(i*c+j) <- s.[j] done
  done;
  cols := c; a)

let solve b =

  let board = array_of_input b in
  let targets = final_box board in
  let solved pos = targets = snd pos in
  let clear = Array.map (function '#' -> '#' | _ -> ' ') in
  let bdc = clear board in
  let q = Queue.create () in
  let pos1 = init_pos board in
  begin
     mark pos1;
     Queue.add (pos1, []) q;
     while not (Queue.is_empty q) do
        let curr, mhist = Queue.pop q in
        let moves = gen_moves curr bdc in
        let check m =
           let next = do_move curr m in
           if not (marked next) then
           if solved next then (show (m::mhist); exit 0)
           else (mark next; Queue.add (next,m::mhist) q) in
        List.iter check moves
     done;
     print_endline "No solution"
  end;;

let level = ["#######";

            "#     #";
            "#     #";
            "#. #  #";
            "#. $$ #";
            "#.$$  #";
            "#.#  @#";
            "#######"] in

solve level</lang> Output:

luULLulDDurrrddlULrruLLrrUruLLLulD

Perl

This performs simultaneous breadth first searches, starting from the initial state and various possible final states, and meeting somewhere in the middle.

On my laptop, which has a slow cpu and little memory, it can solve the basic puzzle in about a second, and a slightly harder one in about 50 seconds.

A slightly more basic version of this code, doing a single breadth first search, took twenty seconds for the basic puzzle, and was unable to solve the slightly harder one before I lost patience with it (about half an hour).

The meet-in-the-middle search uses massively less memory, but obviously more lines of code. Due to the way I alternate between forward and rearward computation, it's possible for the solution to be at most one step longer than the optimal one... but it would still be a valid solution. I could fix it, but at the cost of speed and memory.

<lang Perl>#!perl use strict; use warnings qw(FATAL all); my @initial = split /\n/, <<;

# #
$$$$$$$ @#
....... #

#
#
. # #
. $$ #
.$$ #
.# @#

=for space is an empty square

is a wall

@ is the player $ is a box . is a goal + is the player on a goal

is a box on a goal

=cut

my $cols = length($initial[0]); my $initial = join , @initial; my $size = length($initial); die unless $size == $cols * @initial;

sub WALL() { 1 } sub PLAYER() { 2 } sub BOX() { 4 } sub GOAL() { 8 }

my %input = ( ' ' => 0, '#' => WALL, '@' => PLAYER, '$' => BOX, '.' => GOAL, '+' => PLAYER|GOAL, '*' => BOX|GOAL, ); my %output = reverse(%input);

sub packed_initial { my $ret = ; vec( $ret, $_, 4 ) = $input{substr $initial, $_, 1} for( 0 .. $size-1 ); $ret; }

sub printable_board { my $board = shift; my @c = @output{map vec($board, $_, 4), 0 .. $size-1}; my $ret = ; while( my @row = splice @c, 0, $cols ) { $ret .= join , @row, "\n"; } $ret; }

my $packed = packed_initial();

my @udlr = qw(u d l r); my @UDLR = qw(U D L R); my @deltas = (-$cols, +$cols, -1, +1);

my %fseen; INIT_FORWARD: { $initial =~ /(\@|\+)/ or die; use vars qw(@ftodo @fnext); @ftodo = (["", $packed, $-[0]]); $fseen{$packed} = ; }

my %rseen; INIT_REVERSE: { my $goal = $packed; vec($goal, $ftodo[0][2], 4) -= PLAYER; my @u = grep { my $t = vec($goal, $_, 4); $t & GOAL and not $t & BOX } 0 .. $size-1; my @b = grep { my $t = vec($goal, $_, 4); $t & BOX and not $t & GOAL } 0 .. $size-1; die unless @u == @b; vec($goal, $_, 4) += BOX for @u; vec($goal, $_, 4) -= BOX for @b; use vars qw(@rtodo @rnext); FINAL_PLACE: for my $player (0 .. $size-1) { next if vec($goal, $player, 4); FIND_GOAL: { vec($goal, $player + $_, 4) & GOAL and last FIND_GOAL for @deltas; next FINAL_PLACE; } my $a_goal = $goal; vec($a_goal, $player, 4) += PLAYER; push @rtodo, ["", $a_goal, $player ]; $rseen{$a_goal} = ; #print printable_board($a_goal); } }

my $movelen = -1; my ($solution); MAIN: while( @ftodo and @rtodo ) {

FORWARD: { my ($moves, $level, $player) = @{pop @ftodo}; die unless vec($level, $player, 4) & PLAYER;

for my $dir_num (0 .. 3) { my $delta = $deltas[$dir_num]; my @loc = map $player + $delta * $_, 0 .. 2; my @val = map vec($level, $_, 4), @loc;

next if $val[1] & WALL or ($val[1] & BOX and $val[2] & (BOX|WALL));

my $new = $level; vec($new, $loc[0], 4) -= PLAYER; vec($new, $loc[1], 4) += PLAYER; my $nmoves; if( $val[1] & BOX ) { vec($new, $loc[1], 4) -= BOX; vec($new, $loc[2], 4) += BOX; $nmoves = $moves . $UDLR[$dir_num]; } else { $nmoves = $moves . $udlr[$dir_num]; }

next if exists $fseen{$new}; $fseen{$new} = $nmoves;

push @fnext, [ $nmoves, $new, $loc[1] ];

exists $rseen{$new} or next; #print(($val[1] & BOX) ? "Push $UDLR[$dir_num]\n" : "Fwalk $udlr[$dir_num]\n"); $solution = $new; last MAIN; }

last FORWARD if @ftodo; use vars qw(*ftodo *fnext); (*ftodo, *fnext) = (\@fnext, \@ftodo); } # end FORWARD

BACKWARD: { my ($moves, $level, $player) = @{pop @rtodo}; die "<$level>" unless vec($level, $player, 4) & PLAYER;

for my $dir_num (0 .. 3) { my $delta = $deltas[$dir_num]; # look behind and in front of the player. my @loc = map $player + $delta * $_, -1 .. 1; my @val = map vec($level, $_, 4), @loc;

# unlike the forward solution, we cannot push boxes next if $val[0] & (WALL|BOX); my $new = $level; vec($new, $loc[0], 4) += PLAYER; vec($new, $loc[1], 4) -= PLAYER; # unlike the forward solution, if we have a box behind us # we can *either* pull it or not. This means there are # two "successors" to this board. if( $val[2] & BOX ) { my $pull = $new; vec($pull, $loc[2], 4) -= BOX; vec($pull, $loc[1], 4) += BOX; goto RWALK if exists $rseen{$pull}; my $pmoves = $UDLR[$dir_num] . $moves; $rseen{$pull} = $pmoves; push @rnext, [$pmoves, $pull, $loc[0]]; goto RWALK unless exists $fseen{$pull}; print "Doing pull\n"; $solution = $pull; last MAIN; } RWALK: next if exists $rseen{$new}; # next direction. my $wmoves = $udlr[$dir_num] . $moves; $rseen{$new} = $wmoves; push @rnext, [$wmoves, $new, $loc[0]]; next unless exists $fseen{$new}; print "Rwalk\n"; $solution = $new; last MAIN; }

last BACKWARD if @rtodo; use vars qw(*rtodo *rnext); (*rtodo, *rnext) = (\@rnext, \@rtodo); } # end BACKWARD }

if( $solution ) { my $fmoves = $fseen{$solution}; my $rmoves = $rseen{$solution}; print "Solution found!\n"; print "Time: ", (time() - $^T), " seconds\n"; print "Moves: $fmoves $rmoves\n"; print "Move Length: ", length($fmoves . $rmoves), "\n"; print "Middle Board: \n", printable_board($solution); } else { print "No solution found!\n"; } __END__ </lang>

Output:

Solution found!
Time: 51 seconds
Moves: lldlllllllluurDldRRRRRRRRuulD rdLLLLLLrrrrrurrrdLLLLLLLrrrruulDulDulDulDLLulD
Move Length: 76
Middle Board:
#############
#  #        #
#  $$$$$@   #
#.......$ $ #
#############

On this particular puzzle, the branch factor for the different search directions were clearly quite different, as the forward search only did 29 moves, while the reverse search did 47 moves.

Although my code doesn't print out the actual final board, it would be easy enough to compute from the move list.

Perl 6

Translation of: Go

<lang perl6>sub MAIN() {

   my $level = q:to//;

#
#
. # #
. $$ #
.$$ #
.# @#

   say 'level:';
   print $level;
   say 'solution:';
   say solve($level);

}

class State {

   has Str $.board;
   has Str $.sol;
   has Int $.pos;

   method move(Int $delta --> Str) {
       my $new = $!board;
       if $new.substr($!pos,1) eq '@' {
           substr-rw($new,$!pos,1) = ' ';
       } else {
           substr-rw($new,$!pos,1) = '.';
       }
       my $pos := $!pos + $delta;
       if $new.substr($pos,1) eq ' ' {
           substr-rw($new,$pos,1) = '@';
       } else {
           substr-rw($new,$pos,1) = '+';
       }
       return $new;
   }
    
   method push(Int $delta --> Str) {
       my $pos := $!pos + $delta;
       my $box := $pos + $delta;
       return  unless $!board.substr($box,1) eq ' ' | '.';
       my $new = $!board;
       if $new.substr($!pos,1) eq '@' {
           substr-rw($new,$!pos,1) = ' ';
       } else {
           substr-rw($new,$!pos,1) = '.';
       }
       if $new.substr($pos,1) eq '$' {
           substr-rw($new,$pos,1) = '@';
       } else {
           substr-rw($new,$pos,1) = '+';
       }
       if $new.substr($box,1) eq ' ' {
           substr-rw($new,$box,1) = '$';
       } else {
           substr-rw($new,$box,1) = '*';
       }
       return $new;
   }

}

sub solve(Str $start --> Str) {

   my $board = $start;
   my $width = $board.lines[0].chars + 1;
   my @dirs =
       ["u", "U", -$width],
       ["r", "R", 1],
       ["d", "D", $width],
       ["l", "L", -1];

   my %visited = $board => True;

   my $pos = $board.index('@');
   my @open = State.new(:$board, :sol(), :$pos);
   while @open {
       my $state = @open.shift;
       for @dirs -> [$move, $push, $delta] {
           my $board;
           my $sol;
           my $pos = $state.pos + $delta;
           given $state.board.substr($pos,1) {
               when '$' | '*' {
                   $board = $state.push($delta);
                   next if $board eq "" || %visited{$board};
                   $sol = $state.sol ~ $push;
                   return $sol unless $board ~~ /<[ . + ]>/;
               }
               when ' ' | '.' {
                   $board = $state.move($delta);
                   next if %visited{$board};
                   $sol = $state.sol ~ $move;
               }
               default { next }
           }
           @open.push: State.new: :$board, :$sol, :$pos;
           %visited{$board} = True;
       }
   }
   return "No solution";

}</lang>

Output:

Level:
#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######
Solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD

Phix

Push-optimised, prunes (breadth-first) search space to reachable pushable-to-live boxes.
Fairly fast, but often produces same-push-tally but longer results than move-optimised. <lang Phix>-- demo\rosetta\Sokoban.exw integer w, h -- (set from parsing the input grid) sequence moves -- "", as +/-w and +/-1 (udlr) string live -- "", Y if box can go there

function reachable(sequence pushes, string level)

   integer p = find_any("@+",level)
   string ok = repeat('N',length(level))
   ok[p] = 'Y'
   while true do
       p = find('Y',ok)
       if p=0 then exit end if
       ok[p] = 'y'
       for i=1 to length(moves) do
           integer pn = p+moves[i]
           if ok[pn]='N'
           and find(level[pn]," .") then
               ok[pn] = 'Y'
           end if
       end for
   end while
   for i=length(pushes)-1 to 1 by -2 do
       if ok[pushes[i]-pushes[i+1]]!='y' then
           pushes[i..i+1] = {}
       end if
   end for
   return pushes

end function

function pushable(string level)

   sequence res = {}
   for i=1 to length(level) do
       if find(level[i],"$*") then
           if  find(level[i-w]," .@+")
           and find(level[i+w]," .@+") then
               if live[i-w]='Y' then res &= {i,-w} end if
               if live[i+w]='Y' then res &= {i,+w} end if
           end if
           if  find(level[i-1]," .@+")
           and find(level[i+1]," .@+") then
               if live[i-1]='Y' then res &= {i,-1} end if
               if live[i+1]='Y' then res &= {i,+1} end if
           end if
       end if
   end for
   return reachable(res,level)

end function

function solve(string level)

   atom t2 = time()+2
   integer seen = new_dict()
   sequence solution = "No solution.", partial = {}
   sequence todo = Template:Level,partial,pushable(level), pushes
   while length(todo) do
       sequence t1 = todo[1]
       todo = todo[2..$]
       {level,partial,pushes} = t1
       integer p = find_any("@+",level)
       while length(pushes) do
           integer {s,m} = pushes[1..2]
           pushes = pushes[3..$]
           level[p] = " ."[find(level[p],"@+")]
           level[s] = "@+"[find(level[s],"$*")]
           level[s+m] = "$*"[find(level[s+m]," .")]
           if getd_index(level,seen)=0 then
               sequence np = partial&{s,m}
               if not find('$',level) then
                   solution = np
                   todo = {}
                   pushes = {}
                   exit
               end if
               setd(level,true,seen)
               if time()>t2 then
                   printf(1,"working... (seen %d)\r",dict_size(seen))
                   t2 = time()+2
               end if
               todo = append(todo,{level,np,pushable(level)})
           end if
           level = t1[1] -- (reset)
       end while
   end while
   destroy_dict(seen)
   return solution

end function

procedure plays(string level, sequence solution) -- This plays push-only solutions (see play() for lurd)

   string res = level
   integer p = find_any("@+",level)
   for i=1 to length(solution) by 2 do
       integer {s,m} = solution[i..i+1] m+=s
       level[p] = " ."[find(level[p],"@+")]
       level[s] = "@+"[find(level[s],"$*")]
       level[m] = "$*"[find(level[m]," .")]
       res &= level
       p = s
   end for
   -- (replacing +0 with 1/2/3 may help in some cases)
   puts(1,join_by(split(res,'\n'),h,floor(80/(w+2))+0))

end procedure

procedure mark_live(integer p, string level) -- (idea cribbed from the C version)

   if live[p]='N' then
       live[p] = 'Y'
       integer l = length(level)
       if p-w*2>=1 and level[p-w]!='#' and level[p-w*2]!='#' then mark_live(p-w,level) end if
       if p+w*2<=l and level[p+w]!='#' and level[p+w*2]!='#' then mark_live(p+w,level) end if
       if p-2  >=1 and level[p-1]!='#' and level[p-2]  !='#' then mark_live(p-1,level) end if
       if p+2  <=l and level[p+1]!='#' and level[p+2]  !='#' then mark_live(p+1,level) end if
   end if

end procedure

function make_square(string level) -- -- Sets {h, w, moves, live}, and returns an evened-out/rectangular level --

   if level[$]!='\n' then level &= '\n' end if -- (for the display)
   sequence lines = split(level,'\n')
   h = length(lines)-1             -- set height (ignore trailing \n)
   sequence ln = repeat(0,h)
   for i=1 to h do
       ln[i] = {length(lines[i]),i}
       for j=1 to length(lines[i]) do
           -- validate each line, why not
           if not find(lines[i,j]," #.$@*") then
               crash("invalid input")
           end if
       end for
   end for
   ln = sort(ln)
   w = ln[$][1]+1                  -- set width (==longest, inc \n)
   moves = {-w,+w,-1,+1}           -- and make these (udlr) legal ...
   for i=1 to h do
       integer {l,n} = ln[i], pad = w-1-l
       if pad=0 then exit end if
       lines[n] &= repeat(' ',pad) -- ... by evening up the "grid"
   end for
   level = join(lines,'\n')
   live = join(repeat(repeat('N',w-1),h),'\n')
   for p=1 to length(level) do
       if find(level[p],".+*") then
           mark_live(p,level)
       end if
   end for
   return level

end function

constant input = """

#
#
. # #
. $$ #
.$$ #
.# @#

"""

atom t0 = time() string level = make_square(input) sequence pushset = solve(level) integer pop = length(pushset)/2 if string(pushset) then

   puts(1,level)
   printf(1,"%s\n",{pushset}) -- ("No Solution.")

else

   printf(1,"solution of %d pushes (%s)\n",{pop,elapsed(time()-t0)})
   plays(level,pushset)

end if</lang>

Output:

Note that a full solution in LURD format would show as 48 moves, as opposed to the move-optimal solutions of other entries of 34 moves, but both are 14 pushes.

solution of 14 pushes (0.5s)
#######   #######   #######   #######   #######   #######   #######   #######
#     #   #     #   #     #   #     #   #     #   #     #   #     #   #     #
#     #   #     #   #   $ #   #  $@ #   # $@  #   #$@   #   #@    #   #     #
#. #  #   #. #$ #   #. #@ #   #. #  #   #. #  #   #. #  #   #* #  #   #* #  #
#. $$ #   #. $@ #   #. $  #   #. $  #   #. $  #   #. $  #   #. $  #   #.$@  #
#.$$  #   #.$$  #   #.$$  #   #.$$  #   #.$$  #   #.$$  #   #.$$  #   #.$$  #
#.#  @#   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #   #.#   #
#######   #######   #######   #######   #######   #######   #######   #######

#######   #######   #######   #######   #######   #######   #######
#     #   #     #   #     #   #     #   #     #   #     #   #     #
#     #   #     #   #     #   #     #   #     #   #     #   #     #
#* #  #   #* #  #   #* #  #   #* #  #   #* #  #   #* #  #   #* #  #
#.$$  #   #.$$  #   #.@$  #   #. $  #   #.$@  #   #*@   #   #*    #
#.$@  #   #*@   #   #*$   #   #+$   #   #.$   #   #.$   #   #*@   #
#.#   #   #.#   #   #.#   #   #*#   #   #*#   #   #*#   #   #*#   #
#######   #######   #######   #######   #######   #######   #######

Other tests: <lang Phix>constant input = """

# #
$$$$$$$ @#
....... #

"""</lang>

Output:

solution of 30 pushes (14.6s)
#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
# $$$$$$$  @#   # @$$$$$$   #   #  $$$$$$   #   #  $$$$$$   #   #  $$$$$$   #   #  $$$$$$   #   #  $$$$$$   #   #  $$$$$$   #
#.......    #   #.*.....    #   #.+*....    #   #..+*...    #   #...+*..    #   #....+*.    #   #.....+*    #   #......+$   #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
#  $$$$$$   #   #  $$$$$$   #   #  $@$$$$   #   # $@ $$$$   #   # @  $$$$   #   #    $@$$   #   #   $@ $$   #   #  $@  $$   #
#.......@$  #   #....... @$ #   #...*...  $ #   #...*...  $ #   #.*.*...  $ #   #.*.*.*.  $ #   #.*.*.*.  $ #   #.*.*.*.  $ #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
# $@   $$   #   #$@    $$   #   #@     $$   #   #      $@   #   #     $@    #   #    $@     #   #   $@      #   #   $       #
#.*.*.*.  $ #   #.*.*.*.  $ #   #**.*.*.  $ #   #**.*.*.$ $ #   #**.*.*.$ $ #   #**.*.*.$ $ #   #**.*.*.$ $ #   #***+.*.$ $ #
#############   #############   #############   #############   #############   #############   #############   #############

#############   #############   #############   #############   #############   #############   #############
#  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #   #  #        #
#   @       #   #           #   #           #   #           #   #           #   #           #   #           #
#****.*.$ $ #   #*****+.$ $ #   #*****.*@ $ #   #******+  $ #   #******. $@ #   #******.$@  #   #*******@   #
#############   #############   #############   #############   #############   #############   #############

Test #3 <lang Phix>constant input = """

    ####
   ##. ##

1. 1. 1. 1. . #
# # #
$ # # #
$ @ #
1. 1. 1. 1. ##

    ####

"""</lang>

Output:

solution of 16 pushes (0.0s)
     ####         ####         ####         ####         ####         ####         ####         ####         ####
    ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##       ##. ##
##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### *  #
#   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   # $# #   #   # @# #
# $ #  # #   # @$#  # #   #  $#  # #   #  $#  # #   #  $#  # #   #  $#  # #   #  $# $# #   #  $# @# #   #  $#  # #
# $  @   #   # $      #   # @$     #   #  @$    #   #   @$   #   #    @$  #   #     @  #   #        #   #        #
######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##
     ####         ####         ####         ####         ####         ####         ####         ####         ####

     ####         ####         ####         ####         ####         ####         ####         ####
    ##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##       ##* ##
##### +  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### .  #   ##### *  #
#   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   #  # #   #   # $# #   #   # @# #
#  $#  # #   #  @#  # #   #   #  # #   #   #  # #   #   #  # #   #   # $# #   #   # @# #   #   #  # #
#        #   #  $     #   #  @$    #   #   @$   #   #    @$  #   #     @  #   #        #   #        #
######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##   ######  ##
     ####         ####         ####         ####         ####         ####         ####         ####

Test #4 <lang Phix>constant input = """

... # #
.$$$$$$$ @#
... #

"""</lang>

Output:

"started"
solution of 40 pushes (58.5s)
#############   #############   #############   #############   #############   #############
#... #      #   #... #      #   #.*. #      #   #.** #      #   #.** #      #   #.** #      #
#.$$$$$$$  @#   #.$$@$$$$   #   #.@$ $$$$   #   #. @ $$$$   #   #.   $$$$   #   #.   $$$$   #
#...        #   #...$       #   #...$       #   #...$       #   #...@$      #   #... @$     #
#############   #############   #############   #############   #############   #############
<snip 30 pushes>
#############   #############   #############   #############   #############
#*** #      #   #*** #      #   #*** #      #   #*** #      #   #*** #      #
#*          #   #*          #   #*          #   #*          #   #*          #
#**.   $@   #   #**.  $@    #   #**. $@     #   #**.$@      #   #***@       #
#############   #############   #############   #############   #############

Test #5 <lang Phix>constant input = """

   #####
   #   #
   #   #
 ### #$##
 #      #

1. 1. #$## # ######
# ## ##### .#
$ $ ..#
1. 1. 1. 1. ### #@## .#

   #     #########
   #######

"""</lang>

Output:

solution of 59 pushes (25.5s)
    #####                 #####                 #####                 #####
    #   #                 #   #                 #   #                 #   #
    #   #                 #   #                 #   #                 #   #
  ### #$##              ### #@##              ### # ##              ### # ##
  #      #              #    $ #              #   $@ #              #   $  #
### #$## #   ######   ### #$## #   ######   ### #$## #   ######   ### #@## #   ######
#   # ## #####   .#   #   # ## #####   .#   #   # ## #####   .#   #   #$## #####   .#
# $   $         ..#   # $   $         ..#   # $   $         ..#   # $   $         ..#
##### ### #@##   .#   ##### ### # ##   .#   ##### ### # ##   .#   ##### ### # ##   .#
    #     #########       #     #########       #     #########       #     #########
    #######               #######               #######               #######

<snip 52 pushes>

    #####                 #####                 #####                 #####
    #   #                 #   #                 #   #                 #   #
    #   #                 #   #                 #   #                 #   #
  ### # ##              ### # ##              ### # ##              ### # ##
  #      #              #      #              #      #              #      #
### # ## #   ######   ### # ## #   ######   ### # ## #   ######   ### # ## #   ######
#   # ## #####   *#   #   # ## #####   *#   #   # ## #####   *#   #   # ## #####   *#
#             @$.*#   #              @**#   #               **#   #               **#
##### ### # ## $ .#   ##### ### # ## $ .#   ##### ### # ## @$.#   ##### ### # ##  @*#
    #     #########       #     #########       #     #########       #     #########
    #######               #######               #######               #######

PicoLisp

This searches for a solution, without trying for the push-optimal one. The player moves between the pushes, however, are minimized. <lang PicoLisp>(load "@lib/simul.l")

Display board

(de display ()

  (disp *Board NIL
     '((This)
        (pack
           (if2 (== This *Pos) (memq This *Goals)
              "+"                   # Player on goal
              "@"                   # Player elsewhere
              (if (: val) "*" ".")  # On gloal
              (or (: val) " ") )    # Elsewhere
           " " ) ) ) )

Initialize

(de main (Lst)

  (mapc
     '((B L)
        (mapc
           '((This C)
              (case C
                 (" ")
                 ("." (push '*Goals This))
                 ("@" (setq *Pos This))
                 ("$" (=: val C) (push '*Boxes This))
                 (T (=: val C)) ) )
              B L ) )
     (setq *Board (grid (length (car Lst)) (length Lst)))
     (apply mapcar (flip (mapcar chop Lst)) list) )
  (display) )

Generate possible push-moves

(de pushes ()

  (make
     (for Box *Boxes
        (unless (or (; (west Box) val) (; (east Box) val))
           (when (moves (east Box))
              (link (cons (cons Box (west Box)) *Pos "L" @)) )
           (when (moves (west Box))
              (link (cons (cons Box (east Box)) *Pos "R" @)) ) )
        (unless (or (; (south Box) val) (; (north Box) val))
           (when (moves (north Box))
              (link (cons (cons Box (south Box)) *Pos "D" @)) )
           (when (moves (south Box))
              (link (cons (cons Box (north Box)) *Pos "U" @)) ) ) ) ) )

Moves of player to destination

(de moves (Dst Hist)

  (or
     (== Dst *Pos)
     (mini length
        (extract
           '((Dir)
              (with ((car Dir) Dst)
                 (cond
                    ((== This *Pos) (cons (cdr Dir)))
                    ((: val))
                    ((memq This Hist))
                    ((moves This (cons Dst Hist))
                       (cons (cdr Dir) @) ) ) ) )
           '((west . "r") (east . "l") (south . "u") (north . "d")) ) ) ) )

Find solution

(de go (Res)

  (unless (idx '*Hist (sort (copy *Boxes)) T)  # No repeated state
     (if (find '((This) (<> "$" (: val))) *Goals)
        (pick
           '((Psh)
              (setq  # Move
                 *Pos (caar Psh)
                 *Boxes (cons (cdar Psh) (delq *Pos *Boxes)) )
              (put *Pos 'val NIL)
              (put (cdar Psh) 'val "$")
              (prog1 (go (append (cddr Psh) Res))
                 (setq  # Undo move
                    *Pos (cadr Psh)
                    *Boxes (cons (caar Psh) (delq (cdar Psh) *Boxes)) )
                 (put (cdar Psh) 'val NIL)
                 (put (caar Psh) 'val "$") ) )
           (pushes) )
        (display)  # Display solution
        (pack (flip Res)) ) ) )</lang>

Test: <lang PicoLisp>(main

  (quote
     "#######"
     "#     #"
     "#     #"
     "#. #  #"
     "#. $$ #"
     "#.$$  #"
     "#.#  @#"
     "#######" ) )

(prinl) (go)</lang> Output:

 8 # # # # # # #
 7 #           #
 6 #           #
 5 # .   #     #
 4 # .   $ $   #
 3 # . $ $     #
 2 # . #     @ #
 1 # # # # # # #
   a b c d e f g

 8 # # # # # # #
 7 #           #
 6 # @         #
 5 # *   #     #
 4 # *         #
 3 # *         #
 2 # * #       #
 1 # # # # # # #
   a b c d e f g
-> "uuulDLLulDDurrrrddlUruLLLrrddlUruLdLUUdrruulLulD"

Python

Translation of: D

Works with: Psyco

Works with: Python 2.6

<lang python>from array import array from collections import deque import psyco

data = [] nrows = 0 px = py = 0 sdata = "" ddata = ""

def init(board):

   global data, nrows, sdata, ddata, px, py
   data = filter(None, board.splitlines())
   nrows = max(len(r) for r in data)

   maps = {' ':' ', '.': '.', '@':' ', '#':'#', '$':' '}
   mapd = {' ':' ', '.': ' ', '@':'@', '#':' ', '$':'*'}

   for r, row in enumerate(data):
       for c, ch in enumerate(row):
           sdata += maps[ch]
           ddata += mapd[ch]
           if ch == '@':
               px = c
               py = r

def push(x, y, dx, dy, data):

   if sdata[(y+2*dy) * nrows + x+2*dx] == '#' or \
      data[(y+2*dy) * nrows + x+2*dx] != ' ':
       return None

   data2 = array("c", data)
   data2[y * nrows + x] = ' '
   data2[(y+dy) * nrows + x+dx] = '@'
   data2[(y+2*dy) * nrows + x+2*dx] = '*'
   return data2.tostring()

def is_solved(data):

   for i in xrange(len(data)):
       if (sdata[i] == '.') != (data[i] == '*'):
           return False
   return True

def solve():

   open = deque([(ddata, "", px, py)])
   visited = set([ddata])
   dirs = ((0, -1, 'u', 'U'), ( 1, 0, 'r', 'R'),
           (0,  1, 'd', 'D'), (-1, 0, 'l', 'L'))

   lnrows = nrows
   while open:
       cur, csol, x, y = open.popleft()

       for di in dirs:
           temp = cur
           dx, dy = di[0], di[1]

           if temp[(y+dy) * lnrows + x+dx] == '*':
               temp = push(x, y, dx, dy, temp)
               if temp and temp not in visited:
                   if is_solved(temp):
                       return csol + di[3]
                   open.append((temp, csol + di[3], x+dx, y+dy))
                   visited.add(temp)
           else:
               if sdata[(y+dy) * lnrows + x+dx] == '#' or \
                  temp[(y+dy) * lnrows + x+dx] != ' ':
                   continue

               data2 = array("c", temp)
               data2[y * lnrows + x] = ' '
               data2[(y+dy) * lnrows + x+dx] = '@'
               temp = data2.tostring()

               if temp not in visited:
                   if is_solved(temp):
                       return csol + di[2]
                   open.append((temp, csol + di[2], x+dx, y+dy))
                   visited.add(temp)

   return "No solution"

level = """\

#
#
. # #
. $$ #
.$$ #
.# @#
1. 1. 1. 1. """

psyco.full() init(level) print level, "\n\n", solve()</lang> Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

Runtime: about 0.90 seconds.

Racket

This was originally inspired by PicoLisp's solution. Modified to use a priority queue as mentioned on the Sokoban wiki for the main breadth first search on pushes but just a plain queue for the move bfs. This uses personal libraries. Vector2 isn't strictly needed but the math/array library is not currently optimized for untyped Racket. push! is comparable to lisp's, awhen is anaphoric when, ret uses the bound value as the result of its expression, and tstruct is short for struct with the #:transparent option.

lang racket

(require data/heap

 "../lib/vector2.rkt" "../lib/queue.rkt" (only-in "../lib/util.rkt" push! tstruct ret awhen))

(define level (list "#######"

                   "#     #"
                   "#     #"
                   "#. #  #"
                   "#. $$ #"
                   "#.$$  #"
                   "#.#  @#"
                   "#######"))

(define (strings->vec2 l) (lists->vec2 (map string->list l)))

turn everything except walls into distance from goals

(define (clear-level l)

 (ret ([l (vec2-copy l)])
   (define dots (vec2-atsq l #\.))
   (define q (list->q (map (λ (p) (cons p 0)) dots)))
   (let bfs () ;this search has implicit history in the mutated vector2
     (unless (nilq? q)
       (match-define (cons p n) (deq! q))
       (define x (vec2@ l p))
       ;stop if position is either a wall or a previously filled number
       (cond [(or (eq? x #\#) (number? x)) (bfs)]
             [else (vec2! l p n)
                   (for-adj l x [p p] #f (enq! (cons p (add1 n)) q))
                   (bfs)])))))

corresponds to PicoLisp's move table in "moves", while also adding a push direction mapping

(tstruct move (f d)) (define-values (mu md ml mr LURD)

 (let ()
   (define t (map (λ (x) (cons (car x) (apply pos (cdr x))))
                  '([#\u -1 0] [#\d 1 0] [#\l 0 -1] [#\r 0 1])))
   (define (mv d)
     (define x (assoc d t))
     (move (λ (p) (pos+ p (cdr x))) (car x)))
   (values (mv #\u) (mv #\d) (mv #\l) (mv #\r)
           (λ (d) (char-upcase (car (findf (λ (x) (equal? d (cdr x))) t)))))))

state = player pos * box poses

(tstruct st (p b)) (define (st= s1 s2) (andmap (λ (b) (member b (st-b s2))) (st-b s1))) (define (box? p s) (member p (st-b s)))

calculates value of a state for insertion into priority queue
value is sum of box distances from goals

(define (value s l) (apply + (map (λ (p) (vec2@ l p)) (st-b s))))

init state for a level

(define (st0 l) (st (vec2-atq l #\@) (vec2-atsq l #\$))) (define (make-solution-checker l)

 (define dots (vec2-atsq l #\.))
 (λ (s) (andmap (λ (b) (member b dots)) (st-b s))))

state after push * lurd history

(tstruct push (st h)) (define (pushes s l)

 (ret ([pushes '()])
   (for ([b (in-list (st-b s))])
     (for-adj l a [p b] #f
       (define d (pos- p b)) ;direction of push
       (define op (pos- b d)) ;where player stands to push
       (define o (vec2@ l op))
       ;make sure push pos and push dest are clear
       (when (and (number? a) (number? o)
                  (not (box? p s)) (not (box? op s)))
         (awhen [@ (moves s op l)]
           (define new-st (st b (cons p (remove b (st-b s)))))
           (push! (push new-st (cons (LURD d) @)) pushes)))))))

state * goal pos * level -> lurd string

(define (moves s g l)

 (define h '())
 (define q (list->q (list (list (st-p s)))))
 (let bfs ()
   (if (nilq? q)
       #f
       (match-let ([(cons p lurd) (deq! q)])
         (cond [(equal? p g) lurd]
               [(or (char=? (vec2@ l p) #\#) (box? p s) (member p h)) (bfs)]
               [else (push! p h)
                     (for-each (λ (m)
                                 (match-define (move f s) m)
                                 (enq! (cons (f p) (cons s lurd)) q))
                               (list mu md ml mr))
                     (bfs)])))))

(define (sokoban l)

 (define-values (clear s0 solved?)
   (let ([l (strings->vec2 l)])
     (values (clear-level l) (st0 l) (make-solution-checker l))))
 (define h '())
 (tstruct q-elem (s lurd v)) ;priority queue stores state, lurd hist, and value
 (define (elem<= s1 s2) (<= (q-elem-v s1) (q-elem-v s2))) ;compare wrapped values
 ;queue stores a single element at the beginning consisting of:
 ;1. starting state, 2. empty lurd history, 3. value of starting state
 (define q (vector->heap elem<= (vector (q-elem s0 '() (value s0 clear)))))
 (let bfs ()
   (match-define (q-elem s lurd _) (heap-min q))
   (heap-remove-min! q)
   (cond [(solved? s) (list->string (reverse lurd))]
         [(memf (λ (s1) (st= s s1)) h) (bfs)]
         [else (push! s h)
               (for-each (λ (p)
                           (define s (push-st p))
                           (heap-add! q (q-elem s (append (push-h p) lurd) (value s clear))))
                         (pushes s clear))
               (bfs)])))

</lang>

Output:

Times shown are milliseconds.

> (time (sokoban level))
cpu time: 88 real time: 83 gc time: 0
"uuulDLLrrrddllUdrruulLrrdLuuulldlDDuuurrrddlLrrddlULrruLdlUUdrruulLulD"

Ring

--------------------------------------------------#
Sokoban Game #
2019, Mahmoud Fayed <msfclipper@yahoo.com> #
2019, Gal Zsolt <quiwox@gmail.com>
--------------------------------------------------#

Game Data

aPlayer = [ :Row = 3, :Col = 4 ]

aLevel1 = [ [1,1,1,2,2,2,2,2,1,1,1,1,1,1], [1,2,2,2,1,1,1,2,1,1,1,1,1,1], [1,2,4,3,5,1,1,2,1,1,1,1,1,1], [1,2,2,2,1,5,4,2,1,1,1,1,1,1], [1,2,4,2,2,5,1,2,1,1,1,1,1,1], [1,2,1,2,1,4,1,2,2,1,1,1,1,1], [1,2,5,1,6,5,5,4,2,1,1,1,1,1], [1,2,1,1,1,4,1,1,2,1,1,1,1,1], [1,2,2,2,2,2,2,2,2,1,1,1,1,1], [1,1,1,1,1,1,1,1,1,1,1,1,1,1] ]

aLevel2 = [ [1,1,1,2,2,2,2,2,2,2,2,2,1,1], [1,2,2,2,1,5,1,4,1,1,1,2,1,1], [1,2,4,3,5,1,1,1,5,1,1,2,1,1], [1,2,2,2,1,1,4,1,1,1,1,2,1,1], [1,2,4,2,2,1,5,4,1,5,1,2,1,1], [1,2,1,2,1,4,1,5,1,1,2,2,1,1], [1,2,5,1,6,5,1,4,1,1,1,2,1,1], [1,2,1,1,1,4,1,4,1,5,1,2,1,1], [1,2,2,2,2,2,2,2,2,2,2,2,1,1], [1,1,1,1,1,1,1,1,1,1,1,1,1,1] ]

       aLevel = aLevel1

nActiveLevel = 1

# For Game Restart aLevel1Copy = aLevel1 aLevel2Copy = aLevel2 aPlayerCopy = aPlayer

C_LEVEL_ROWSCOUNT = 10 C_LEVEL_COLSCOUNT = 14

C_EMPTY = 1 C_WALL = 2 C_PLAYER = 3 C_DOOR = 4 C_BOX = 5 C_BOXONDOOR = 6 C_PLAYERONDOOR = 7

nKeyClock = clock()

# Will be used when moving a Box aCurrentBox = [ :Row = 0, :Col = 0 ] nRowDiff = 0 nColDiff = 0

# When the player win lPlayerWin = False

load "gameengine.ring"

func main

oGame = New Game {

title = "Sokoban"

Map {

blockwidth = 60 blockheight = 60

aMap = aLevel

aImages = [ "images/empty.jpg", "images/wall.jpg", "images/player.jpg", "images/door.jpg", "images/box.jpg", "images/boxondoor.jpg", "images/player.jpg" # Player on Door ]

keypress = func oGame,oSelf,nkey { # Avoid getting many keys in short time if (clock() - nKeyClock) < clockspersecond()/4 return ok nKeyClock = Clock() Switch nkey on Key_Esc oGame.Shutdown() on Key_Space # Restart the Level if nActiveLevel = 1 aLevel = aLevel1Copy else aLevel = aLevel2Copy ok aPlayer = aPlayerCopy UpdateGameMap(oGame) lPlayerWin = False on Key_Right if aPlayer[:col] < C_LEVEL_COLSCOUNT nRowDiff = 0 nColDiff = 1 MoveObject(oGame,PlayerType(),aPlayer[:row],aPlayer[:col]+1) ok on Key_Left if aPlayer[:col] > 1 nRowDiff = 0 nColDiff = -1 MoveObject(oGame,PlayerType(),aPlayer[:row],aPlayer[:col]-1) ok on Key_Up if aPlayer[:row] > 1 nRowDiff = -1 nColDiff = 0 MoveObject(oGame,PlayerType(),aPlayer[:row]-1,aPlayer[:col]) ok on Key_Down if aPlayer[:row] < C_LEVEL_ROWSCOUNT nRowDiff = 1 nColDiff = 0 MoveObject(oGame,PlayerType(),aPlayer[:row]+1,aPlayer[:col]) ok off if lPlayerWin = False if CheckWin() lPlayerWin = True DisplayYouWin(oGame) ok ok }

}

text { x = 70 y=550 animate = false size = 20 file = "fonts/pirulen.ttf" text = "Level:" color = rgb(0,0,0) }

               NewButton(oGame,180,550,150,30,"Level 1",:Click1)
               NewButton(oGame,350,550,150,30,"Level 2",:Click2)

}

func MoveObject oGame,nObjectType,nNewRow,nNewCol lMove = False switch nObjectType on C_PLAYER switch aLevel[nNewRow][nNewCol] on C_EMPTY aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_PLAYER UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True on C_DOOR aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True on C_BOX aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff) aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_PLAYER UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True ok on C_BOXONDOOR aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff) aLevel[aPlayer[:row]][aPlayer[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True ok off on C_PLAYERONDOOR switch aLevel[nNewRow][nNewCol] on C_EMPTY aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_PLAYER UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True on C_DOOR aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_PLAYERONDOOR UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True on C_BOX aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff) aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_PLAYER UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True ok on C_BOXONDOOR aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff) aLevel[aPlayer[:row]][aPlayer[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_PLAYER UpdateGameMap(oGame) aPlayer[:row] = nNewRow aPlayer[:col] = nNewCol lMove = True ok off on C_BOX switch aLevel[nNewRow][nNewCol] on C_EMPTY aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_BOX UpdateGameMap(oGame) lMove = True on C_DOOR aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_BOXONDOOR UpdateGameMap(oGame) lMove = True on C_BOX aOldBox = aCurrentBox aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff) aCurrentBox = aOldBox aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_BOX UpdateGameMap(oGame) lMove = True ok on C_BOXONDOOR aOldBox = aCurrentBox aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff) aCurrentBox = aOldBox aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_EMPTY aLevel[nNewRow][nNewCol] = C_BOXONDOOR UpdateGameMap(oGame) lMove = True ok off on C_BOXONDOOR switch aLevel[nNewRow][nNewCol] on C_EMPTY aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_BOX UpdateGameMap(oGame) lMove = True on C_DOOR aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_BOXONDOOR UpdateGameMap(oGame) lMove = True on C_BOX aOldBox = aCurrentBox aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOX,nNewRow+nRowDiff,nNewCol+nColDiff) aCurrentBox = aOldBox aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_BOX UpdateGameMap(oGame) lMove = True ok on C_BOXONDOOR aOldBox = aCurrentBox aCurrentBox[:row] = nNewRow aCurrentBox[:col] = nNewCol if MoveObject(oGame,C_BOXONDOOR,nNewRow+nRowDiff,nNewCol+nColDiff) aCurrentBox = aOldBox aLevel[aCurrentBox[:row]][aCurrentBox[:col]] = C_DOOR aLevel[nNewRow][nNewCol] = C_BOXONDOOR UpdateGameMap(oGame) lMove = True ok

off off return lMove

func UpdateGameMap oGame # The Map is our first object in Game Objects oGame.aObjects[1].aMap = aLevel

func PlayerType # It could be (Player) or (Player on door) return aLevel[aPlayer[:row]][aPlayer[:col]]

func CheckWin for aRow in aLevel if find(aRow,C_DOOR) or find(aRow,C_PLAYERONDOOR) return False ok next return True

func DisplayYouWin oGame oGame {

         text {
               point = 400
               size = 30
               nStep = 9
               file = "fonts/pirulen.ttf"
               text = "You Win !!!"
               x = 500  y=10

state = func ogame,oself { if oself.y >= 400 ogame.remove(oSelf.nIndex) ok }

         }
       }

func NewButton oGame,nX,nY,nWidth,nHeight,cText,cFunc

   oGame {
       Object {
                       x = nX y=nY width = nWidth height=nHeight
           AddAttribute(self,:Text)
           AddAttribute(self,:EventCode)
           Text = cText
           EventCode = cFunc
                       draw = func oGame,oSelf {
                               oSelf {
                   gl_draw_filled_rectangle(x,y,x+width,y+height,gl_map_rgb(0,100,255))
                   gl_draw_rectangle(x,y,x+width,y+height,gl_map_rgb(0,0,0),2)
                   oFont = oResources.LoadFont("fonts/pirulen.ttf",20)
                   gl_draw_text(oFont,gl_map_rgb(0,0,0),x+width/2,y+5,1,Text)
               }
           }
           mouse = func oGame,oSelf,nType,aMouseList {
               if nType = GE_MOUSE_UP
                   MouseX = aMouseList[GE_MOUSE_X]
                   MouseY = aMouseList[GE_MOUSE_Y]
                   oSelf {
                       if MouseX >= x and MouseX <= X+270 and
                          MouseY >= y and MouseY <= Y+40        
                              call EventCode(oGame,oSelf)
                       ok  
                   }
               ok
           }
       }
   }
   return len(oGame.aObjects)

func Click1 oGame,oSelf aLevel = aLevel1 nActiveLevel = 1 aPlayer = aPlayerCopy UpdateGameMap(oGame) lPlayerWin = False

func Click2 oGame,oSelf aLevel = aLevel2 nActiveLevel = 2 aPlayer = aPlayerCopy UpdateGameMap(oGame) lPlayerWin = False </lang>

Ruby

Simple Version

Translation of: Python

<lang ruby>require 'set'

class Sokoban

 def initialize(level)
   board = level.each_line.map(&:rstrip)
   @nrows = board.map(&:size).max
   board.map!{|line| line.ljust(@nrows)}
   board.each_with_index do |row, r|
     row.each_char.with_index do |ch, c|
       @px, @py = c, r  if ch == '@' or ch == '+'
     end
   end
   @goal = board.join.tr(' .@#$+*', ' .   ..')
                .each_char.with_index.select{|ch, c| ch == '.'}
                .map(&:last)
   @board = board.join.tr(' .@#$+*', '  @#$ $')
 end
 
 def pos(x, y)
   y * @nrows + x
 end
 
 def push(x, y, dx, dy, board)         # modify board
   return  if board[pos(x+2*dx, y+2*dy)] != ' '
   board[pos(x     , y     )] = ' '
   board[pos(x + dx, y + dy)] = '@'
   board[pos(x+2*dx, y+2*dy)] = '$'
 end
 
 def solved?(board)
   @goal.all?{|i| board[i] == '$'}
 end
 
 DIRS = [[0, -1, 'u', 'U'], [ 1, 0, 'r', 'R'], [0,  1, 'd', 'D'], [-1, 0, 'l', 'L']]
 def solve
   queue = @board, "", @px, @py
   visited = Set[@board]
   
   until queue.empty?
     current, csol, x, y = queue.shift
     
     for dx, dy, cmove, cpush in DIRS
       work = current.dup
       case work[pos(x+dx, y+dy)]      # next character
       when '$'
         next  unless push(x, y, dx, dy, work)
         next  unless visited.add?(work)
         return csol+cpush  if solved?(work)
         queue << [work, csol+cpush, x+dx, y+dy]
       when ' '
         work[pos(x, y)]       = ' '
         work[pos(x+dx, y+dy)] = '@'
         queue << [work, csol+cmove, x+dx, y+dy]  if visited.add?(work)
       end
     end
   end
   "No solution"
 end

end</lang> Test: <lang ruby>level = <<EOS

#
#
. # #
. $$ #
.$$ #
.# @#

EOS puts level, "", Sokoban.new(level).solve</lang>

Output:

#######
#     #
#     #
#. #  #
#. $$ #
#.$$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD

Runtime: about 3.2 seconds.

Faster Version

It examines beforehand the place where the box can not move to the goal. When a box is pushed there, it doesn't process after that.

<lang ruby>class Sokoban

 def initialize(level)
   board = level.lines.map(&:rstrip)
   leng  = board.map(&:length).max
   board = board.map{|line| line.ljust(leng)}.join
   @goal = []
   board.each_char.with_index do |c, i|
     @player = i  if c == '@' or c == '+'
     @goal << i   if c == '.' or c == '+' or c == '*'
   end
   @board = board.tr(' .@#$+*', '  @#$ $')
   @lurd = [[-1, 'l', 'L'], [-leng, 'u', 'U'], [1, 'r', 'R'], [leng, 'd', 'D']]
   @dirs = @lurd.map(&:first)
   set_dead_zone(board.tr('^#', ' '))
 end
 
 def set_dead_zone(wall)
   corner = search_corner(wall)
   @dead = corner.dup
   begin
     size = @dead.size
     corner.each do |pos|
       @dirs.each do |dir|
         next  if wall[pos + dir] == '#'
         @dead.concat(check_side(wall, pos+dir, dir))
       end
     end
   end until size == @dead.size
 end
 
 def search_corner(wall)
   wall.size.times.with_object([]) do |i, corner|
     next  if wall[i] == '#' or @goal.include?(i)
     case count_wall(wall, i)
     when 2
       corner << i  if wall[i-1] != wall[i+1]
     when 3
       corner << i
     end
   end
 end
 
 def check_side(wall, pos, dir)
   wk = []
   until wall[pos] == '#' or count_wall(wall, pos) == 0 or @goal.include?(pos)
     return wk if @dead.include?(pos)
     wk << pos
     pos += dir
   end
   []
 end
 
 def count_wall(wall, pos)
   @dirs.count{|dir| wall[pos + dir] == '#'}
 end
 
 def push_box(pos, dir, board)
   return board  if board[pos + 2*dir] != ' '
   board[pos        ] = ' '
   board[pos +   dir] = '@'
   board[pos + 2*dir] = '$'
   board
 end
 
 def solved?(board)
   @goal.all?{|i| board[i] == '$'}
 end
 
 def solve
   queue = @board, "", @player
   # When the key doesn't exist in Hash, it subscribes a key but it returns false.
   visited = Hash.new{|h,k| h[k]=true; false}
   visited[@board]                     # first subscription
   
   until queue.empty?
     board, route, pos = queue.shift
     @lurd.each do |dir, move, push|
       work = board.dup
       case work[pos+dir]
       when '$'    # push
         work = push_box(pos, dir, work)
         next  if visited[work]
         return route+push  if solved?(work)
         queue << [work, route+push, pos+dir]  unless @dead.include?(pos+2*dir)
       when ' '    # move
         work[pos    ] = ' '
         work[pos+dir] = '@'
         next  if visited[work]
         queue << [work, route+move, pos+dir]
       end
     end
   end
   "No solution"
 end

end</lang> Runtime: about 0.20 seconds.

Tcl

This code does a breadth-first search so it finds a solution with a minimum number of moves.

Translation of: OCaml

<lang tcl>package require Tcl 8.5

proc solveSokoban b {

   set cols [string length [lindex $b 0]]
   set dxes [list [expr {-$cols}] $cols -1 1]
   set i 0
   foreach c [split [join $b ""] ""] {

switch $c { " " {lappend bdc " "} "#" {lappend bdc "#"} "@" {lappend bdc " ";set startplayer $i } "$" {lappend bdc " ";lappend startbox $i} "." {lappend bdc " "; lappend targets $i} "+" {lappend bdc " ";set startplayer $i; lappend targets $i} "*" {lappend bdc " ";lappend startbox $i;lappend targets $i} } incr i

   }
   set q [list [list $startplayer $startbox] {}]
   set store([lindex $q 0]) {}
   for {set idx 0} {$idx < [llength $q]} {incr idx 2} {

lassign [lindex $q $idx] x boxes foreach dir {U D L R} dx $dxes { if {[set x1 [expr {$x + $dx}]] in $boxes} { if {[lindex $bdc [incr x1 $dx]] ne " " || $x1 in $boxes} { continue } set tmpboxes $boxes set x1 [expr {$x + $dx}] for {set i 0} {$i < [llength $boxes]} {incr i} { if {[lindex $boxes $i] == $x1} { lset tmpboxes $i [expr {$x1 + $dx}] break } } if {$dx == 1 || $dx == -1} { set next [list $x1 $tmpboxes] } else { set next [list $x1 [lsort -integer $tmpboxes]] } if {![info exists store($next)]} { if {$targets eq [lindex $next 1]} { foreach c [lindex $q [expr {$idx + 1}]] { lassign $c ispush olddir if {$ispush} { append solution $olddir } else { append solution [string tolower $olddir] } } return [append solution $dir] } set store($next) {} set nm [lindex $q [expr {$idx + 1}]] lappend q $next lappend q [lappend nm [list 1 $dir]] } } elseif {[lindex $bdc $x1] eq " "} { set next [list [expr {$x + $dx}] $boxes] if {![info exists store($next)]} { set store($next) {} set nm [lindex $q [expr {$idx + 1}]] lappend q $next lappend q [lappend nm [list 0 $dir]] } } }

   }
   error "no solution"

}</lang> Demonstration code: <lang tcl>set level {

   "#######"
   "#     #"
   "#     #"
   "#. #  #"
   "#. $$ #"
   "#.$$  #"
   "#.#  @#"
   "#######"

} puts [solveSokoban $level]</lang>

Output:

ulULLulDDurrrddlULrruLLrrUruLLLulD

Runtime with stock Tcl 8.5 installation: ≅2.2 seconds