add sliding puzzle script.

Author: everthis

773-sliding-puzzle.js

@@ -0,0 +1,51 @@
+/**
+ * @param {number[][]} board
+ * @return {number}
+ */
+const slidingPuzzle = function(board) {
+  const target = "123450";
+  let start = "";
+  for (let i = 0; i < board.length; i++) {
+    for (let j = 0; j < board[0].length; j++) {
+      start += board[i][j];
+    }
+  }
+  const visited = {};
+  // all the positions 0 can be swapped to
+  const dirs = [[1, 3], [0, 2, 4], [1, 5], [0, 4], [1, 3, 5], [2, 4]];
+  const queue = [];
+  queue.push(start);
+  visited[start] = true;
+  let res = 0;
+  while (queue.length !== 0) {
+    // level count, has to use size control here, otherwise not needed
+    let size = queue.length;
+    for (let i = 0; i < size; i++) {
+      let cur = queue.shift();
+      if (cur === target) {
+        return res;
+      }
+      let zero = cur.indexOf("0");
+      // swap if possible
+      for (let dir of dirs[zero]) {
+        let next = swap(cur, zero, dir);
+        if (visited.hasOwnProperty(next)) {
+          continue;
+        }
+        visited[next] = true;
+        queue.push(next);
+      }
+    }
+    res++;
+  }
+  return -1;
+};
+
+function swap(str, i, j) {
+  const arr = str.split("");
+  const ic = str[i];
+  const jc = str[j];
+  arr.splice(i, 1, jc);
+  arr.splice(j, 1, ic);
+  return arr.join("");
+}