52 N皇后 II

class Solution {
public:
    void print_board(const vector<string> &ch) {
        int _pos = 0;
        cout << "棋盘:" << endl;
        for (const auto &x:ch)
            cout << "  " << x << endl;
    }

    void set(vector<string> &board, vector<string> &ch, int x, int y, int n) {
        constexpr static int dx[] = {-1, 0, 1, -1, 1, -1, 0, 1};
        constexpr static int dy[] = {-1, -1, -1, 0, 0, 1, 1, 1};
        board[y][x] = 'Q';
        ch[y][x] = 'Q';
        for (int orien = 0; orien < 8; ++orien) {
            for (int _x = x + dx[orien], _y = y + dy[orien];
                 _x >= 0 && _x < n && _y >= 0 && _y < n; _x += dx[orien], _y += dy[orien])
                if (board[_y][_x] != 'Q')
                    board[_y][_x] = 'Q';
        }
    }

    void reset(vector<string> &board, vector<string> &ch, int x, int y, int n) {
        constexpr static int dx[] = {-1, 0, 1, -1, 1, -1, 0, 1};
        constexpr static int dy[] = {-1, -1, -1, 0, 0, 1, 1, 1};
        board[y][x] = '.';
        ch[y][x] = '.';
        for (int orien = 0; orien < 8; ++orien) {
            for (int _x = x + dx[orien], _y = y + dy[orien];
                 _x >= 0 && _x < n && _y >= 0 && _y < n; _x += dx[orien], _y += dy[orien])
                if (board[_y][_x] != '.')
                    board[_y][_x] = '.';
        }
    }

    void solve(int &ans, vector<string> ch, vector<string> _ch, int x, int y, int n) {
        if (y == n) {
            ++ans;
            return;
        }
        for (; x < n; ++x)
            if (ch[y][x] != 'Q') {
                set(ch, _ch, x, y, n);
                solve(ans, ch, _ch, x + 1, y + 1, n);
                reset(ch, _ch, x, y, n);
            }
    }

    int totalNQueens(int n) {
        int ans = 0;
        string t(n, '.');
        vector<string> _ch(n, t), ch(_ch);
//        for (auto &x:ch)
//            cout << x << endl;
        solve(ans, ch, _ch, 0, 0, n);
        cout << ans;
        return ans;
    }
};