Find common directory path
You are encouraged to solve this task according to the task description, using any language you may know.
Create a routine that, given a set of strings representing directory paths and a single character directory separator, will return a string representing that part of the directory tree that is common to all the directories.
Test your routine using the forward slash '/' character as the directory separator and the following three strings as input paths:
'/home/user1/tmp/coverage/test' '/home/user1/tmp/covert/operator' '/home/user1/tmp/coven/members'
Note: The resultant path should be the valid directory '/home/user1/tmp'
and not the longest common string '/home/user1/tmp/cove'
.
If your language has a routine that performs this function (even if it does not have a changeable separator character, then mention it as part of the task)
Ada
<lang ada> with Ada.Text_IO; use Ada.Text_IO;
procedure Test_Common_Path is
function "rem" (A, B : String) return String is Slash : Integer := A'First; -- At the last slash seen in A At_A : Integer := A'first; At_B : Integer := B'first; begin loop if At_A > A'Last then if At_B > B'Last or else B (At_B) = '/' then return A; else return A (A'First..Slash - 1); end if; elsif At_B > B'Last then if A (At_A) = '/' then -- A cannot be shorter than B here return B; else return A (A'First..Slash - 1); end if; elsif A (At_A) /= B (At_B) then return A (A'First..Slash - 1); elsif A (At_A) = '/' then Slash := At_A; end if; At_A := At_A + 1; At_B := At_B + 1; end loop; end "rem";
begin
Put_Line ( "/home/user1/tmp/coverage/test" rem "/home/user1/tmp/covert/operator" rem "/home/user1/tmp/coven/members" );
end Test_Common_Path; </lang> Output:
/home/user1/tmp
ALGOL 68
<lang algol68># Utilities code #
CHAR dir sep = "/"; # Assume POSIX #
PROC dir name = (STRING dir)STRING: (
STRING out; FOR pos FROM UPB dir BY -1 TO LWB dir DO IF dir[pos] = dir sep THEN out := dir[:pos-1]; GO TO out exit FI OD; # else: # out:=""; out exit: out
);
PROC shortest = ([]STRING string list)STRING: (
INT min := max int; INT min key := LWB string list - 1; FOR key FROM LWB string list TO UPB string list DO IF UPB string list[key][@1] < min THEN min := UPB string list[key][@1]; min key := key FI OD; string list[min key]
);
- Actual code #
PROC common prefix = ([]STRING strings)STRING: (
IF LWB strings EQ UPB strings THEN # exit: # strings[LWB strings] ELSE STRING prefix := shortest(strings); FOR pos FROM LWB prefix TO UPB prefix DO CHAR first = prefix[pos]; FOR key FROM LWB strings+1 TO UPB strings DO IF strings[key][@1][pos] NE first THEN prefix := prefix[:pos-1]; GO TO prefix exit FI OD OD; prefix exit: prefix FI
);
- Test code #
test:(
[]STRING dir list = ( "/home/user1/tmp/coverage/test", "/home/user1/tmp/covert/operator", "/home/user1/tmp/coven/members" ); print((dir name(common prefix(dir list)), new line))
)</lang> Output:
/home/user1/tmp
AutoHotkey
<lang autohotkey>Dir1 := "/home/user1/tmp/coverage/test" Dir2 := "/home/user1/tmp/covert/operator" Dir3 := "/home/user1/tmp/coven/members"
StringSplit, Dir1_, Dir1, / StringSplit, Dir2_, Dir2, / StringSplit, Dir3_, Dir3, /
Loop
If (Dir1_%A_Index% = Dir2_%A_Index%) And (Dir1_%A_Index% = Dir3_%A_Index%) Result .= (A_Index=1 ? "" : "/") Dir1_%A_Index% Else Break
MsgBox, % Result</lang> Message box shows:
/home/user1/tmp
C
- This code specimen retains the original ALGOL 68 coding style.
note: This code uses the gcc block expression C language extension: ({ ~ }) <lang c>#include <stdlib.h>
- include <stdio.h>
- include <string.h>
- include <limits.h>
/* Utilities code */
char dir_sep = '/'; /* Assume POSIX */
- define LWB(s) 0 /* default C lower bound */
- define STRUPB(s) (strlen(s)) /* NUL terminated char* upper bound */
/* find upper bound of a NULL terminated list - ({ ~ }) gcc extension */
- define LISTUPB(list) ({ int i; for(i=0; list[i]!=NULL; i++); i-1; })
char *str_slice(char *s, int lwb, int upb){
char *new = malloc(upb-lwb+2); strncpy(new, s+lwb, upb-lwb+2); new[upb+1] = '\0'; return new;
}
char *dir_name(char *dir){
char *out; int pos; for(pos = STRUPB(dir); pos>=LWB(dir); pos--){ if(dir[pos] == dir_sep){ out = str_slice(dir,LWB(dir),pos-1); return out; } } return "";
}
char *shortest (char *string_list[]){
int min = INT_MAX; int min_key = LWB(string_list) - 1; int key; for(key = LWB(string_list); string_list[key]; key++){ if(STRUPB(string_list[key]) < min){ min = STRUPB(string_list[key]) - LWB(string_list[key]); min_key = key; } } return string_list[min_key];
}
/* Actual code */
char *common_prefix(char *strings[]){
if(LWB(strings) == LISTUPB(strings)){ /* exit: */ return strings[LWB(strings)]; } else { char *prefix = shortest(strings); int pos; for(pos = LWB(prefix); prefix[pos]; pos++){ char first = prefix[pos]; int key; for(key = LWB(strings)+1; strings[key]; key++){ if(strings[key][pos] != first){ prefix = str_slice(prefix, LWB(prefix), pos-1); return prefix; } } } return prefix ; }
}
/* Test code */
main(){
char *dir_list[] = { "/home/user1/tmp/coverage/test", "/home/user1/tmp/covert/operator", "/home/user1/tmp/coven/members", NULL }; printf("%s\n",dir_name(common_prefix(dir_list)));
}</lang> Output:
/home/user1/tmp
Clojure
<lang clojure>(defn common-prefix [sep paths]
(let [parts-per-path (map #(.split (re-pattern sep) %) paths) common-parts (for [part-list (apply map vector parts-per-path) :while (apply = part-list)] (first part-list))] (apply str (interpose sep common-parts))))
(println
(common-prefix "/" ["/home/user1/tmp/coverage/test" "/home/user1/tmp/covert/operator" "/home/user1/tmp/coven/members"]))</lang>
C#
<lang csharp> using System; using System.Collections.Generic; using System.Linq; using System.Text;
namespace RosettaCodeTasks {
class Program { static void Main ( string[ ] args ) { FindCommonDirectoryPath.Test ( ); }
}
class FindCommonDirectoryPath { public static void Test ( ) { Console.WriteLine ( "Find Common Directory Path" ); Console.WriteLine ( ); List<string> PathSet1 = new List<string> ( ); PathSet1.Add ( "/home/user1/tmp/coverage/test" ); PathSet1.Add ( "/home/user1/tmp/covert/operator" ); PathSet1.Add ( "/home/user1/tmp/coven/members" ); Console.WriteLine("Path Set 1 (All Absolute Paths):"); foreach ( string path in PathSet1 ) { Console.WriteLine ( path ); } Console.WriteLine ( "Path Set 1 Common Path: {0}", FindCommonPath ( "/", PathSet1 ) ); } public static string FindCommonPath ( string Separator, List<string> Paths ) { string CommonPath = String.Empty; List<string> SeparatedPath = Paths .First ( str => str.Length == Paths.Max ( st2 => st2.Length ) ) .Split ( new string[ ] { Separator }, StringSplitOptions.RemoveEmptyEntries ) .ToList ( );
foreach ( string PathSegment in SeparatedPath.AsEnumerable ( ) ) { if ( CommonPath.Length == 0 && Paths.All ( str => str.StartsWith ( PathSegment ) ) ) { CommonPath = PathSegment; } else if ( Paths.All ( str => str.StartsWith ( CommonPath + Separator + PathSegment ) ) ) { CommonPath += Separator + PathSegment; } else { break; } }
return CommonPath; } } }
</lang>
Factor
<lang factor>: take-shorter ( seq1 seq2 -- shorter )
[ shorter? ] 2keep ? ;
- common-head ( seq1 seq2 -- head )
2dup mismatch [ nip head ] [ take-shorter ] if* ;
- common-prefix-1 ( file1 file2 separator -- prefix )
[ common-head ] dip '[ _ = not ] trim-tail ;
- common-prefix ( seq separator -- prefix )
[ ] swap '[ _ common-prefix-1 ] map-reduce ;</lang>
( scratchpad ) { "/home/user1/tmp/coverage/test" "/home/user1/tmp/covert/operator" "/home/user1/tmp/coven/members" } CHAR: / common-prefix . "/home/user1/tmp/"
J
Solution: <lang j>parseDirs =: = <;.2 ] getCommonPrefix =: {. ;@{.~ 0 i.~ *./@(="1 {.)
getCommonDirPath=: [: getCommonPrefix parseDirs&></lang>
Example: <lang j> paths=: '/home/user1/tmp/coverage/test';'/home/user1/tmp/covert/operator';'/home/user1/tmp/coven/members'
getCommonPrefix >paths
/home/user1/tmp/cove
'/' getCommonDirPath paths
/home/user1/tmp/</lang>
Note: This alternative formulation of parseDirs provides cross-platform support, without the need to specify the path separator. <lang j>parseDirs =: (PATHSEP_j_&= <;.2 ])@jhostpath</lang>
OCaml
<lang ocaml>let rec aux acc paths =
if List.mem [] paths then (List.rev acc) else let heads = List.map List.hd paths in let item = List.hd heads in let all_the_same = List.for_all ((=) item) (List.tl heads) in if all_the_same then aux (item::acc) (List.map List.tl paths) else (List.rev acc)
let common_prefix sep = function
| [] -> invalid_arg "common_prefix" | dirs -> let paths = List.map (Str.split (Str.regexp_string sep)) dirs in let res = aux [] paths in (sep ^ (String.concat sep res))
let () =
let dirs = [ "/home/user1/tmp/coverage/test"; "/home/user1/tmp/covert/operator"; "/home/user1/tmp/coven/members"; ] in print_endline (common_prefix "/" dirs);
- </lang>
(uses the module Str
, str.cma)
Oz
With a few helper functions, we can express the solution like this in Oz: <lang oz>declare
fun {CommonPrefix Sep Paths} fun {GetParts P} {String.tokens P Sep} end Parts = {ZipN {Map Paths GetParts}} EqualParts = {List.takeWhile Parts fun {$ X|Xr} {All Xr {Equals X}} end} in {Join Sep {Map EqualParts Head}} end
fun {ZipN Xs} if {Some Xs {Equals nil}} then nil else {Map Xs Head} | {ZipN {Map Xs Tail}} end end
fun {Join Sep Xs} {FoldR Xs fun {$ X Z} {Append X Sep|Z} end nil} end
fun {Equals C} fun {$ X} X == C end end
fun {Head X|_} X end
fun {Tail _|Xr} Xr end
in
{System.showInfo {CommonPrefix &/ ["/home/user1/tmp/coverage/test" "/home/user1/tmp/covert/operator" "/home/user1/tmp/coven/members"]}}</lang>
PicoLisp
<lang PicoLisp>(de commonPath (Lst Chr)
(glue Chr (make (apply find (mapcar '((L) (split (chop L) Chr)) Lst) '(@ (or (pass <>) (nil (link (next))))) ) ) ) )</lang>
Output:
(commonPath (quote "/home/user1/tmp/coverage/test" "/home/user1/tmp/covert/operator" "/home/user1/tmp/coven/members" ) "/" ) -> "/home/user1/tmp"
PureBasic
PureBasic don't have a path comparator directly but instead have powerful string tools.
Simply by checking the catalog names until they mismatch and add up the correct parts, the task is accomplished. <lang PureBasic>Procedure.s CommonPath(Array InPaths.s(1),separator.s="/")
Protected SOut$="" Protected i, j, toggle If ArraySize(InPaths())=0 ProcedureReturn InPaths(0) ; Special case, only one path EndIf Repeat i+1 toggle=#False For j=1 To ArraySize(InPaths()) If (StringField(InPaths(j-1),i,separator)=StringField(InPaths(j),i,separator)) If Not toggle SOut$+StringField(InPaths(j-1),i,separator)+separator toggle=#True EndIf Else ProcedureReturn SOut$ EndIf Next ForEver
EndProcedure</lang>
Example of implementation <lang PureBasic>Dim t.s(2) t(0)="/home/user1/tmp/coverage/test" t(1)="/home/user1/tmp/covert/operator" t(2)="/home/user1/tmp/coven/members"
Debug CommonPath(t(),"/"))</lang>
Python
The Python os.path.commonprefix function is broken as it returns common characters that may not form a valid directory path: <lang python>>>> import os >>> os.path.commonprefix(['/home/user1/tmp/coverage/test',
'/home/user1/tmp/covert/operator', '/home/user1/tmp/coven/members'])
'/home/user1/tmp/cove'</lang>
This result can be fixed: <lang python>>>> def commonprefix(*args, sep='/'): return os.path.commonprefix(*args).rpartition(sep)[0]
>>> commonprefix(['/home/user1/tmp/coverage/test',
'/home/user1/tmp/covert/operator', '/home/user1/tmp/coven/members'])
'/home/user1/tmp'</lang>
But it may be better to not rely on the faulty implementation at all: <lang python>>>> from itertools import takewhile >>> def allnamesequal(name): return all(n==name[0] for n in name[1:])
>>> def commonprefix(paths, sep='/'): bydirectorylevels = zip(*[p.split(sep) for p in paths]) return sep.join(x[0] for x in takewhile(allnamesequal, bydirectorylevels))
>>> commonprefix(['/home/user1/tmp/coverage/test',
'/home/user1/tmp/covert/operator', '/home/user1/tmp/coven/members'])
'/home/user1/tmp'</lang>
Ruby
Uses the standard library abbrev
module: Given a set of strings, calculate the set of unambiguous abbreviations for those strings, and return a hash where the keys are all the possible abbreviations and the values are the full strings.
<lang ruby>require 'abbrev'
dirs = %w( /home/user1/tmp/coverage/test /home/user1/tmp/covert/operator /home/user1/tmp/coven/members )
common_prefix = dirs.abbrev.keys.min_by {|key| key.length}.chop # => "/home/user1/tmp/cove" common_directory = common_prefix.sub(%r{/[^/]*$}, ) # => "/home/user1/tmp"</lang>
Implementing without that module: <lang ruby>separator = '/' paths = dirs.collect {|dir| dir.split(separator)} uncommon_idx = paths.transpose.each_with_index.find {|dirnames, idx| dirnames.uniq.length > 1}.last common_directory = paths[0][0 ... uncommon_idx].join(separator) # => "/home/user1/tmp"</lang>
Tcl
<lang tcl>package require Tcl 8.5 proc pop {varname} {
upvar 1 $varname var set var [lassign $var head] return $head
}
proc common_prefix {dirs {separator "/"}} {
set parts [split [pop dirs] $separator] while {[llength $dirs]} { set r {} foreach cmp $parts elt [split [pop dirs] $separator] { if {$cmp ne $elt} break lappend r $cmp } set parts $r } return [join $parts $separator]
}</lang>
% common_prefix {/home/user1/tmp/coverage/test /home/user1/tmp/covert/operator /home/user1/tmp/coven/members} /home/user1/tmp
Ursala
The algorithm is to lex the paths into component directory names, and then find the greatest common prefix of those. <lang Ursala>#import std
comdir"s" "p" = mat"s" reduce(gcp,0) (map sep "s") "p"</lang>
where "s"
is a dummy variable representing the separator, "p"
is a dummy variable representing the list of paths, and
sep
is second order function in the standard library that takes a separator character and returns a lexer mapping a string containing the separator to a list of the substrings found between occurrences of itmap
is the conventional mapping combinator, which takes a function operating on items of a list to a function operating pointwise on a whole listgcp
is a polymorphic greatest-common-prefix library function working on pairs of strings or lists of any typereduce
is the standard functional programming reduction combinator, which cumulatively applies a binary operator to a list of operands given the operator and the vacuous case resultmat
is a second order function in the standard library that takes a separator character and returns a function that flattens a list of strings into a single string with copies of the separator inserted between them
Here is a version using operators instead of mnemonics for map
and reduce
.
<lang Ursala>comdir"s" "p" = mat"s" gcp:-0 sep"s"* "p"</lang>
Here is one in partly point-free form, using the composition operator (+
).
<lang Ursala>comdir"s" = mat"s"+ gcp:-0+ sep"s"*</lang>
Here it is in point-free form.
<lang Ursala>comdir = +^/mat gcp:-0++ *+ sep</lang>
test program:
<lang Ursala>#cast %s
test =
comdir`/ <
'/home/user1/tmp/coverage/test', '/home/user1/tmp/covert/operator', '/home/user1/tmp/coven/members'></lang>
output:
'/home/user1/tmp'