Leetcode 52. N皇后 II

和上一题一摸一样，只是返回上一题答案的size

class Solution {
public:
    int ans;
    bool vis[1005][1005] = {}, row[1005] = {};
    void dfs(int col, int &n) {
        if (col == n) {
            ++ans;
            return;
        }
        for (int i = 0; i < n; ++i)
            if (!row[i] && !vis[i][col]) {
                vectorint, 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 = 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;
                dfs(col + 1, n);
                for (auto &x : tt)
                    vis[x.first][x.second] = 0;
                row[i] = 0;
            }

    }
    int totalNQueens(int n) {
        dfs(0, n);
        return ans;
    }
};