June 2018 Update

Task/Sokoban/Kotlin/sokoban.kotlin

@@ -0,0 +1,116 @@
+// 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())
+}