class Solution {private:    int queen_num;    int total;public:    int totalNQueens(int n) {        queen_num = n;        total = 0;        vector
     
       h(n, false);        vector
      
        v(n, false);        vector
       
         lx(n * 2 + 1, false);        vector
        
          rx(n * 2 + 1, false);        dfs(0, h, v, lx, rx);        return total;    }    void dfs(int level, vector
         
           &h, vector
          
            &v, vector
           
             &lx, vector
            
              &rx) { if (level == queen_num) { total++; return; } int row = level; int col = 0; while (col < queen_num) { if (!h[row] && !v[col] && !lx[row + col] && !rx[row + queen_num - col - 1]) { h[row] = v[col] = lx[row + col] = rx[row + queen_num - col - 1] = true; dfs(level + 1, h, v, lx, rx); h[row] = v[col] = lx[row + col] = rx[row + queen_num - col - 1] = false; } col++; } }};
            
           
          
         
        
       
      
     

或许可以用状态压缩？