Leetcode 51. N皇后

暴力深搜

class Solution {
public:
    vector<vector<string>> ans;
    vector<string> tmp;
    bool vis[1005][1005] = {}, row[1005] = {};
    void dfs(int col, int &n) {
        if (col == n) {
            ans.push_back(tmp);
            return;
        }
        for (int i = 0; i < n; ++i)
            if (!row[i] && !vis[i][col]) {
                vector<pair<int, int>> tt;
                row[i] = 1;
                int k = 1;
                while (col + k < n && i + k < n) {
                    if (!vis[i + k][col + k])
                        tt.push_back(make_pair(i + k, col + k));
                    ++k;
                }
                k = 1;
                while (col + k <n && i - k >= 0) {
                    if (!vis[i - k][col + k])
                        tt.push_back(make_pair(i - k, col + k));
                    ++k;
                }
                for (auto &x : tt)
                    vis[x.first][x.second] = 1;
                tmp[i][col] = 'Q';
                dfs(col + 1, n);
                tmp[i][col] = '.';
                for (auto &x : tt)
                    vis[x.first][x.second] = 0;
                row[i] = 0;
            }

    }
    vector<vector<string>> solveNQueens(int n) {
        tmp.assign(n, string(n, '.'));
        dfs(0, n);
        return ans;
    }
};