leetcode-----51. N皇后

• 链接：https://leetcode-cn.com/problems/n-queens/

代码

class Solution {
public:
    int N;
    vector<bool> col, dg, udg;
    vector<vector<string>> ans;
    vector<string> path;

    vector<vector<string>> solveNQueens(int n) {
        N = n;
        col = vector<bool>(N);
        dg = udg = vector<bool>(N * 2);
        path = vector<string>(N, string(n, '.'));

        dfs(0);
        return ans;     
    }

    void dfs(int u) {
        if (u == N) {
            ans.push_back(path);
            return ;
        }
        for (int i = 0; i < N; ++i) {
            if (!col[i] && !dg[u - i + N] && !udg[u + i]) {
                col[i] = dg[u - i + N] = udg[u + i] = true;
                path[u][i] = 'Q';
                dfs(u + 1);
                path[u][i] = '.';
                col[i] = dg[u - i + N] = udg[u + i] = false;                 
            }
        }
    }
};