# Sokoban

Sokoban
You are encouraged to solve this task according to the task description, using any language you may know.

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.

## 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.

`#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; inlinestate_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;} inlinevoid unnewstate(state_t *p) {	p->next = block_head;	block_head = p;} enum { space, wall, player, box }; #define E "\033["const char * const glyph1[] = { " ", "#", E"[email protected]"E"m", E"33m\$"E"m"};const char * const glyph2[] = { E"32m."E"m", "#", E"[email protected]"E"m", E"32m\$"E"m"};#undef E // mark up positions where a box definitely should not bevoid 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 functioninlinevoid 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;}`

## 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.

`#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;}`

Output:

```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

### Unordered Set-based Version

Works with: C++11
Works with: Boost
Works with: GCC 4.6

`#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<Table>> 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;}`

## C#

`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());        }    }}`

Output:

```Level:

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

Solution:

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## D

### Shorter Version

Translation of: C++

This version uses the queue defined in the Queue/Usage task.

`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(" #[email protected]*"), "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 ="########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @########";     immutable b = immutable(Board)(level.splitLines);    writeln(level, "\n\n", b.solve);}`
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.

`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;}`

## Elixir

Works with: Elixir version 1.3
Translation of: Ruby
`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)  endend level = """########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @########"""IO.puts levelSokoban.solve(level)`
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.

`package main import (    "fmt"    "strings") func main() {    level := `########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @########`    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)}`
Output:
```level:
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD
```

`import Control.Monad (liftM)import Data.Arrayimport Data.List (transpose)import Data.Maybe (mapMaybe)import qualified Data.Sequence as Seqimport qualified Data.Set as Setimport Prelude hiding (Left, Right) data Field = Space | Wall | Goal           deriving (Eq) data Action = Up | Down | Left | Right | PushUp | PushDown | PushLeft | PushRight 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 Fieldtype BoxArray = Array Index Booltype PlayerPos = Indextype GameState = (BoxArray, PlayerPos)type Game = (FieldArray, GameState) toField :: Char -> FieldtoField '#' = WalltoField ' ' = SpacetoField '@' = SpacetoField '\$' = SpacetoField '.' = GoaltoField '+' = GoaltoField '*' = Goal toPush :: Action -> ActiontoPush Up    = PushUptoPush Down  = PushDowntoPush Left  = PushLefttoPush Right = PushRighttoPush n     = n toMove :: Action -> IndextoMove 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] -> GameparseGame 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`
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## Java

Translation of C++ via D

Works with: Java version 7
`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());    }}`
`ulULLulDDurrrddlULrruLLrrUruLLLulD`

## Kotlin

Translation of: Java
`// 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())}`
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```

## OCaml

Translation of: Python

This uses a breadth-first move search, so will find a move-optimal solution.

`type dir = U | D | L | Rtype 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 0let delta = function U -> -(!cols) | D -> !cols | L -> -1 | R -> 1 let store = Hashtbl.create 251let 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 = ["#######";             "#     #";             "#     #";             "#. #  #";             "#. \$\$ #";             "#.\$\$  #";             "#.#  @#";             "#######"] insolve level`

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.

`#!perluse strict;use warnings qw(FATAL all);my @initial = split /\n/, <<'';##############  #        ## \$\$\$\$\$\$\$  @##.......    ############## ########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @######## =forspace 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__ `
Output:
```Solution found!
Time: 51 seconds
Moves: lldlllllllluurDldRRRRRRRRuulD rdLLLLLLrrrrrurrrdLLLLLLLrrrruulDulDulDulDLLulD
Move Length: 76
Middle Board:
#############
#  #        #
#  [email protected]   #
#.......\$ \$ #
#############
```

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
`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";}`
Output:
```Level:
#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######
Solution:
ulULLulDDurrrddlULrruLLrrUruLLLulD```

## PicoLisp

This searches for a solution, without trying for the push-optimal one. The player moves between the pushes, however, are minimized.

`(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)) ) ) )`

Test:

`(main   (quote      "#######"      "#     #"      "#     #"      "#. #  #"      "#. \$\$ #"      "#.\$\$  #"      "#.#  @#"      "#######" ) )(prinl)(go)`

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
`from array import arrayfrom collections import dequeimport psyco data = []nrows = 0px = py = 0sdata = ""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 = """\########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @########""" psyco.full()init(level)print level, "\n\n", solve()`

Output:

```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD```

## 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 ([email protected] 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) ([email protected] 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 ([email protected] 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=? ([email protected] 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)]))) `
Output:

Times shown are milliseconds.

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

## Ruby

### Simple Version

Translation of: Python
`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(' [email protected]#\$+*', ' .   ..')                 .each_char.with_index.select{|ch, c| ch == '.'}                 .map(&:last)    @board = board.join.tr(' [email protected]#\$+*', '  @#\$ \$')  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"  endend`

Test:

`level = <<EOS########     ##     ##. #  ##. \$\$ ##.\$\$  ##.#  @########EOSputs level, "", Sokoban.new(level).solve`
Output:
```#######
#     #
#     #
#. #  #
#. \$\$ #
#.\$\$  #
#.#  @#
#######

ulULLulDDurrrddlULrruLLrrUruLLLulD
```

### 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.

`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(' [email protected]#\$+*', '  @#\$ \$')    @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"  endend`

## Tcl

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

Translation of: OCaml
`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"}`

Demonstration code:

`set level {    "#######"    "#     #"    "#     #"    "#. #  #"    "#. \$\$ #"    "#.\$\$  #"    "#.#  @#"    "#######"}puts [solveSokoban \$level]`
Output:
`ulULLulDDurrrddlULrruLLrrUruLLLulD`

Runtime with stock Tcl 8.5 installation: ≅2.2 seconds