力扣 困难 52.N皇后II

题目介绍

题解

法一：返回51题N皇后List的长度
法二：

class Solution {private int n, ans;private boolean[] onPath, diag1, diag2;public int totalNQueens(int n) {this.n = n;onPath = new boolean[n];diag1 = new boolean[n * 2 - 1];diag2 = new boolean[n * 2 - 1];dfs(0);return ans;}private void dfs(int r) {if (r == n) {ans++; // 找到一个合法方案return;}for (int c = 0; c < n; c++) {int rc = r - c + n - 1;if (!onPath[c] && !diag1[r + c] && !diag2[rc]) {onPath[c] = diag1[r + c] = diag2[rc] = true;dfs(r + 1);onPath[c] = diag1[r + c] = diag2[rc] = false; // 恢复现场}}}
}