Update 51-n-queens.js

Author: everthis

51-n-queens.js

@@ -1,3 +1,47 @@
+/**
+ * @param {number} n
+ * @return {string[][]}
+ */
+const solveNQueens = function(n) {
+  const res = []
+  const chess = Array.from({length: n}, () => new Array(n).fill('.'))
+  bt(res, chess, 0)
+  return res
+}
+
+function bt(res, chess, row) {
+  if(row === chess.length) {
+    res.push(build(chess))
+    return
+  }
+  for(let i = 0, num = chess[0].length; i < num; i++) {
+    if(valid(chess, row, i)) {
+      chess[row][i] = 'Q'
+      bt(res, chess, row + 1)
+      chess[row][i] = '.'
+    }
+  }
+}
+
+function valid(chess, row, col) {
+  for(let i = row - 1; i >= 0; i--) {
+    if(chess[i][col] === 'Q') return false
+  }
+  for(let i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
+    if(chess[i][j] === 'Q') return false
+  }
+  for(let i = row - 1, j = col + 1; i >= 0 && j < chess[0].length; i--, j++) {
+    if(chess[i][j] === 'Q') return false
+  }
+  return true
+}
+
+function build(chess) {
+  return chess.map(el => el.join(''))
+}
+
+// another
+
 /**
  * @param {number} n
  * @return {string[][]}