N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

 

和上题几乎一样，还简单点。

1 class Solution { 2 private: 3   int res; 4 public: 5   int totalNQueens(int n) { 6     vector
     
       state(n, -1); 7     res = 0; 8     helper(state, 0); 9     return res;10   }11   void helper(vector
      
        &state, int row)12   {13     int n = state.size();14     if(row == n)15     {16       res++;17       return;18     }19     for(int col = 0; col < n; col++)20       if(isValid(state, row, col))21       {22         state[row] = col;23         helper(state, row+1);24         state[row] = -1;25       }26   }27   bool isValid(vector
       
         &state, int row, int col)28   {29     for(int i = 0; i < row; i++)30       if(state[i] == col || abs(row - i) == abs(col - state[i]))31         return false;32     return true;33   }34 35 };