Sorting algorithms/Pancake sort: Difference between revisions
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=={{header|JavaScript}}== |
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<lang javascript>Array.prototype.pancake_sort = function () { |
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for (var i = this.length - 1; i >= 1; i--) { |
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// find the index of the largest element not yes sorted |
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var max_idx = 0; |
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var max = this[0]; |
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for (var j = 1; j <= i; j++) { |
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if (this[j] > max) { |
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max = this[j]; |
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max_idx = j; |
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} |
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} |
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if (max_idx == i) |
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continue; // element already in place |
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var new_slice; |
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// flip this max element to index 0 |
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if (max_idx > 0) { |
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new_slice = this.slice(0, max_idx+1).reverse(); |
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for (var j = 0; j <= max_idx; j++) |
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this[j] = new_slice[j]; |
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} |
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// then flip the max element to its place |
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new_slice = this.slice(0, i+1).reverse(); |
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for (var j = 0; j <= i; j++) |
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this[j] = new_slice[j]; |
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} |
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return this; |
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} |
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ary = [7,6,5,9,8,4,3,1,2,0] |
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sorted = ary.concat().pancake_sort();</lang> |
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=={{header|OCaml}}== |
=={{header|OCaml}}== |
Revision as of 14:26, 17 April 2010
You are encouraged to solve this task according to the task description, using any language you may know.
Sorting Algorithm
This is a sorting algorithm. It may be applied to a set of data in order to sort it.
For comparing various sorts, see compare sorts.
For other sorting algorithms, see sorting algorithms, or:
Heap sort | Merge sort | Patience sort | Quick sort
O(n log2n) sorts
Shell Sort
O(n2) sorts
Bubble sort |
Cocktail sort |
Cocktail sort with shifting bounds |
Comb sort |
Cycle sort |
Gnome sort |
Insertion sort |
Selection sort |
Strand sort
other sorts
Bead sort |
Bogo sort |
Common sorted list |
Composite structures sort |
Custom comparator sort |
Counting sort |
Disjoint sublist sort |
External sort |
Jort sort |
Lexicographical sort |
Natural sorting |
Order by pair comparisons |
Order disjoint list items |
Order two numerical lists |
Object identifier (OID) sort |
Pancake sort |
Quickselect |
Permutation sort |
Radix sort |
Ranking methods |
Remove duplicate elements |
Sleep sort |
Stooge sort |
[Sort letters of a string] |
Three variable sort |
Topological sort |
Tree sort
Sort an array of integers (of any convenient size) into ascending order using Pancake sorting. In short, instead of individual elements being sorted, the only operation allowed is to "flip" one end of the list, like so:
Before: 6 7 8 9 2 5 3 4 1 After: 9 8 7 6 2 5 3 4 1
Only one end of the list can be flipped; this should be the low end, but the high end is okay if it's easier to code or works better.
Show both the initial, unsorted list and the final sorted list. (Intermediate steps during sorting are optional.) Optimizations are optional (but recommended).
For more information on pancake sorting, see the Wikipedia entry.
See also: Number reversal game
BASIC
<lang qbasic>RANDOMIZE TIMER
DIM nums(9) AS INTEGER DIM L0 AS INTEGER, L1 AS INTEGER, n AS INTEGER
'initial values FOR L0 = 0 TO 9
nums(L0) = L0
NEXT 'scramble FOR L0 = 9 TO 1 STEP -1
n = INT(RND * (L0)) + 1 IF n <> L0 THEN SWAP nums(n), nums(L0)
NEXT 'display initial condition FOR L0 = 0 TO 9
PRINT nums(L0);
NEXT PRINT
FOR L1 = 9 TO 1 STEP -1
n = 0 FOR L0 = 1 TO L1 IF nums(n) < nums(L0) THEN n = L0 NEXT
IF (n < L1) THEN IF (n > 0) THEN FOR L0 = 0 TO (n \ 2) SWAP nums(L0), nums(n - L0) NEXT FOR L0 = 0 TO 9 PRINT nums(L0); NEXT PRINT END IF FOR L0 = 0 TO (L1 \ 2) SWAP nums(L0), nums(L1 - L0) NEXT
FOR L0 = 0 TO 9 PRINT nums(L0); NEXT PRINT END IF
NEXT</lang>
Sample output:
0 4 6 1 8 7 2 5 3 9 8 1 6 4 0 7 2 5 3 9 3 5 2 7 0 4 6 1 8 9 7 2 5 3 0 4 6 1 8 9 1 6 4 0 3 5 2 7 8 9 6 1 4 0 3 5 2 7 8 9 2 5 3 0 4 1 6 7 8 9 5 2 3 0 4 1 6 7 8 9 1 4 0 3 2 5 6 7 8 9 4 1 0 3 2 5 6 7 8 9 2 3 0 1 4 5 6 7 8 9 3 2 0 1 4 5 6 7 8 9 1 0 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
JavaScript
<lang javascript>Array.prototype.pancake_sort = function () {
for (var i = this.length - 1; i >= 1; i--) { // find the index of the largest element not yes sorted var max_idx = 0; var max = this[0]; for (var j = 1; j <= i; j++) { if (this[j] > max) { max = this[j]; max_idx = j; } }
if (max_idx == i) continue; // element already in place
var new_slice;
// flip this max element to index 0 if (max_idx > 0) { new_slice = this.slice(0, max_idx+1).reverse(); for (var j = 0; j <= max_idx; j++) this[j] = new_slice[j]; }
// then flip the max element to its place new_slice = this.slice(0, i+1).reverse(); for (var j = 0; j <= i; j++) this[j] = new_slice[j]; } return this;
} ary = [7,6,5,9,8,4,3,1,2,0] sorted = ary.concat().pancake_sort();</lang>
OCaml
<lang ocaml>let rec sorted = function
| [] -> (true) | x::y::_ when x > y -> (false) | x::xs -> sorted xs
let rev_until_max li =
let rec aux acc greater prefix suffix = function | x::xs when x > greater -> aux (x::acc) x acc xs xs | x::xs -> aux (x::acc) greater prefix suffix xs | [] -> (greater, (prefix @ suffix)) in aux [] min_int [] li li
let pancake_sort li =
let rec aux i li suffix = let greater, li = rev_until_max li in let suffix = greater :: suffix and li = List.rev li in if sorted li then (li @ suffix), i else aux (succ i) li suffix in aux 0 li []
let print_list li =
List.iter (Printf.printf " %d") li; print_newline()
let make_rand_list n bound =
let rec aux acc i = if i >= n then (acc) else aux ((Random.int bound)::acc) (succ i) in aux [] 0
let () =
Random.self_init(); let li = make_rand_list 8 100 in print_list li; let res, n = pancake_sort li in print_list res; Printf.printf " sorted in %d loops\n" n;
- </lang>
PureBasic
<lang PureBasic>If OpenConsole()
Define i, j, k, Loops Dim Pile(9) ;-------------------------------------------------------------- ;- Create a Random Pile() For i=1 To 9 ;- Initiate the Pile Pile(i)=i Next For i=0 To 50 ;- Mix it up Swap Pile(Random(8)+1),Pile(Random(8)+1) Next Print("Original Pile() :") For i=1 To 9 Print(" "+str(Pile(i))) Next ;-------------------------------------------------------------- ;- Start Sorting For i=9 To 2 Step -1 If Pile(i)<>i ;- Only Flip it if the current cake need Swapping Loops+1 j=0 Repeat ;- find place of Pancake(i) in the Pile() j+1 Until Pile(j)=i For k=1 To (j/2) ;- Flip it up Swap Pile(k),Pile(j-k+1) Next For k=1 To i/2 ;- Flip in place Swap Pile(k),Pile(i-k+1) Next EndIf Next Print(#CRLF$+"Resulting Pile() :") For i=1 To 9 Print(" "+str(Pile(i))) Next Print(#CRLF$+"All done in "+str(Loops)+" loops.") Print(#CRLF$+#CRLF$+"Press ENTER to quit."): Input() CloseConsole()
EndIf</lang>
Output can look like
Original Pile() : 9 4 1 8 6 3 2 5 7 Resulting Pile() : 1 2 3 4 5 6 7 8 9 All done in 6 loops. Press ENTER to quit.
Python
The function: <lang python>tutor = False
def pancakesort(data):
if len(data) <= 1: return data if tutor: print() for size in range(len(data), 1, -1): maxindex = max(range(size), key=data.__getitem__) if maxindex+1 != size: # This indexed max needs moving if maxindex != 0: # Flip the max item to the left if tutor: print('With: %r doflip %i' % ( ' '.join(str(x) for x in data), maxindex+1 )) data[:maxindex+1] = reversed(data[:maxindex+1]) # Flip it into its final position if tutor: print('With: %r doflip %i' % ( ' '.join(str(x) for x in data), size )) data[:size] = reversed(data[:size]) if tutor: print()</lang>
A test: <lang python>if __name__ == '__main__':
import random
tutor = True data = list('123456789') while data == sorted(data): random.shuffle(data) print('Original List: %r' % ' '.join(data)) pancakesort(data) print('Pancake Sorted List: %r' % ' '.join(data))</lang>
Sample output:
Original List: '6 7 2 1 8 9 5 3 4' With: '6 7 2 1 8 9 5 3 4' doflip 6 With: '9 8 1 2 7 6 5 3 4' doflip 9 With: '4 3 5 6 7 2 1 8 9' doflip 5 With: '7 6 5 3 4 2 1 8 9' doflip 7 With: '1 2 4 3 5 6 7 8 9' doflip 3 With: '4 2 1 3 5 6 7 8 9' doflip 4 With: '3 1 2 4 5 6 7 8 9' doflip 3 With: '2 1 3 4 5 6 7 8 9' doflip 2 Pancake Sorted List: '1 2 3 4 5 6 7 8 9'
Ruby
<lang ruby>class Array
def pancake_sort! num_flips = 0 self.size.downto(2) do |i| end_idx = i - 1 max_idx = self[0..end_idx].each_with_index.max_by {|e| e[0]}.last next if max_idx == end_idx
if max_idx > 0 self[0..max_idx] = self[0..max_idx].reverse
if $DEBUG num_flips += 1 p [num_flips, self] end end
self[0..end_idx] = self[0..end_idx].reverse
if $DEBUG num_flips += 1 p [num_flips, self] end end
self end
end
p a = (1..9).to_a.shuffle p a.pancake_sort!</lang>
sample output:
$ ruby -d sorting_pancake.rb [7, 3, 6, 8, 2, 4, 5, 1, 9] [1, [8, 6, 3, 7, 2, 4, 5, 1, 9]] [2, [1, 5, 4, 2, 7, 3, 6, 8, 9]] [3, [7, 2, 4, 5, 1, 3, 6, 8, 9]] [4, [6, 3, 1, 5, 4, 2, 7, 8, 9]] [5, [2, 4, 5, 1, 3, 6, 7, 8, 9]] [6, [5, 4, 2, 1, 3, 6, 7, 8, 9]] [7, [3, 1, 2, 4, 5, 6, 7, 8, 9]] [8, [2, 1, 3, 4, 5, 6, 7, 8, 9]] [9, [1, 2, 3, 4, 5, 6, 7, 8, 9]] [1, 2, 3, 4, 5, 6, 7, 8, 9]
Tcl
<lang tcl>package require Tcl 8.5
- Some simple helper procedures
proc flip {nlist n} {
concat [lreverse [lrange $nlist 0 $n]] [lrange $nlist $n+1 end]
} proc findmax {nlist limit} {
lsearch -exact $nlist [tcl::mathfunc::max {*}[lrange $nlist 0 $limit]]
}
- Simple-minded pancake sort algorithm
proc pancakeSort {nlist {debug ""}} {
for {set i [llength $nlist]} {[incr i -1] > 0} {} {
set j [findmax $nlist $i] if {$i != $j} { if {$j} { set nlist [flip $nlist $j] if {$debug eq "debug"} {puts [incr flips]>>$nlist} } set nlist [flip $nlist $i] if {$debug eq "debug"} {puts [incr flips]>>$nlist} }
} return $nlist
}</lang> Demonstrate (with debug mode enabled so it prints intermediate states): <lang tcl>puts [pancakeSort {27916 5928 23535 14711 32184 14621 21093 14422 29844 11093} debug]</lang> Output:
1>>32184 14711 23535 5928 27916 14621 21093 14422 29844 11093 2>>11093 29844 14422 21093 14621 27916 5928 23535 14711 32184 3>>29844 11093 14422 21093 14621 27916 5928 23535 14711 32184 4>>14711 23535 5928 27916 14621 21093 14422 11093 29844 32184 5>>27916 5928 23535 14711 14621 21093 14422 11093 29844 32184 6>>11093 14422 21093 14621 14711 23535 5928 27916 29844 32184 7>>23535 14711 14621 21093 14422 11093 5928 27916 29844 32184 8>>5928 11093 14422 21093 14621 14711 23535 27916 29844 32184 9>>21093 14422 11093 5928 14621 14711 23535 27916 29844 32184 10>>14711 14621 5928 11093 14422 21093 23535 27916 29844 32184 11>>14422 11093 5928 14621 14711 21093 23535 27916 29844 32184 12>>5928 11093 14422 14621 14711 21093 23535 27916 29844 32184 5928 11093 14422 14621 14711 21093 23535 27916 29844 32184
As you can see, it took 12 flips.