kt: add «773. Sliding Puzzle»

URL:	https://leetcode.com/problems/sliding-puzzle/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/sliding-puzzle.kt

@@ -0,0 +1,63 @@
+class Solution {
+    companion object {
+        private val DIRECTIONS: List<List<Int>> =
+            listOf(
+                listOf(1, 3),
+                listOf(0, 2, 4),
+                listOf(1, 5),
+                listOf(0, 4),
+                listOf(1, 3, 5),
+                listOf(2, 4),
+            )
+        private val TARGET: String = "123450"
+
+        private fun swap(
+            board: String,
+            i: Int,
+            j: Int,
+        ): String {
+            val cells = board.toMutableList()
+
+            val tmp = cells[i]
+            cells[i] = cells[j]
+            cells[j] = tmp
+
+            return cells.joinToString(separator = "")
+        }
+    }
+
+    fun slidingPuzzle(board: Array<IntArray>): Int {
+        val startState =
+            board.flatMap { it.asSequence() }.joinToString(separator = "") {
+                it.toString()
+            }
+
+        val seen = mutableSetOf<String>(startState)
+        val queue = ArrayDeque<String>(listOf(startState))
+
+        var moves = 0
+        while (queue.isNotEmpty()) {
+            for (i in 1..queue.size) {
+                val current = queue.removeFirst()
+                if (current == TARGET) {
+                    return moves
+                }
+
+                val zeroIdx = current.indexOf('0')
+                DIRECTIONS[zeroIdx].forEach {
+                    val next = swap(current, zeroIdx, it)
+                    if (seen.contains(next)) {
+                        return@forEach
+                    }
+
+                    seen.add(next)
+                    queue.addLast(next)
+                }
+            }
+
+            moves += 1
+        }
+
+        return -1
+    }
+}