leetCode51.N皇后

题解分析

代码

class Solution {
public:
    int n;
    vector<vector<string>> ans;
    vector<string> path;
    vector<bool> col, dg,udg;
    vector<vector<string>> solveNQueens(int _n) {
        n = _n;
        col = vector<bool> (n);
        dg = udg = vector<bool> (2 * n);
        path = vector<string> (n, string(n,'.'));

        dfs(0);
        return ans;
    }

    void dfs(int y){
        if(y == n){
            ans.push_back(path);
            return;
        }

        for(int x = 0; x < n; x++){
            if(!col[x] && !dg[y - x + n] && !udg[y + x]){
                col[x] = dg[y - x + n] = udg[y + x] = true;
                path[y][x] = 'Q';
                dfs(y + 1);
                path[y][x] = '.';
                col[x] = dg[y - x + n] = udg[y + x] = false;
            }
        }
    }
};