LeetCode 51.N皇后

/**
 * @param {number} n
 * @return {string[][]}
 */
var solveNQueens = function (n) {
    const visn = Array(n).fill(false); //列
    const visne = Array(n * 2).fill(false); //正对角线
    const visnw = Array(n * 2).fill(false); //反对角线
    const ans = [],
        plan = [];
    for (let i = 0; i < n; i++) plan.push(Array(n).fill('.'));
    function dfs(r) {
        if (r == n) {
            ans.push(plan.map((i) => i.join('')));
            return;
        }
        for (let c = 0; c < n; c++) {
            if (!visn[c] && !visne[r + c] && !visnw[n + r - c]) {
                visn[c] = visne[r + c] = visnw[n + r - c] = true;
                plan[r][c] = 'Q';
                dfs(r + 1);
                visn[c] = visne[r + c] = visnw[n + r - c] = false;
                plan[r][c] = '.';
            }
        }
    }
    dfs(0);
    return ans;
};