Add solution #51

Author: JoshCrozier

0051-n-queens.js

@@ -0,0 +1,42 @@
+/**
+ * 51. N-Queens
+ * https://leetcode.com/problems/n-queens/
+ * Difficulty: Hard
+ *
+ * The n-queens puzzle is the problem of placing n queens on an n x n
+ * chessboard such that no two queens attack each other.
+ *
+ * Given an integer n, return all distinct solutions to the n-queens
+ * puzzle. You may return the answer in any order.
+ *
+ * Each solution contains a distinct board configuration of the n-queens'
+ * placement, where 'Q' and '.' both indicate a queen and an empty space,
+ * respectively.
+ */
+
+/**
+ * @param {number} n
+ * @return {string[][]}
+ */
+var solveNQueens = function(n) {
+  const result = [];
+  backtrack(result, n);
+  return result;
+};
+
+function backtrack(result, n, board = [], size = 0) {
+  if (n === size) {
+    result.push(board.map(s => `${'.'.repeat(s)}Q${'.'.repeat(n - s - 1)}`));
+  } else {
+    for (let rows = 0; rows < n; rows++) {
+      const isValid = !board.some((i, j) => {
+        return i === rows || i === rows + size - j || i === rows - size + j;
+      });
+      if (isValid) {
+        board.push(rows);
+        backtrack(result, n, board, size + 1);
+        board.pop();
+      }
+    }
+  }
+}

README.md

@@ -56,6 +56,7 @@
 48|[Rotate Image](./0048-rotate-image.js)|Medium|
 49|[Group Anagrams](./0049-group-anagrams.js)|Medium|
 50|[Pow(x, n)](./0050-powx-n.js)|Medium|
+51|[N-Queens](./0051-n-queens.js)|Hard|
 53|[Maximum Subarray](./0053-maximum-subarray.js)|Easy|
 54|[Spiral Matrix](./0054-spiral-matrix.js)|Medium|
 57|[Insert Interval](./0057-insert-interval.js)|Medium|