leetcode 52. N-Queens II

 1 int totalNQueens(int n) 
 2     {
 3         int solutions = 0;
 4         if (n <= 0)
 5             return solutions;
 6         vector<int> mark(n, 0);
 7         
 8         NQueen(mark, n, 0, solutions);
 9         return solutions;
10     }
11     
12     void NQueen(vector<int> &mark, int n, int row, int &solutions)
13     {
14         if (row == n)
15         {
16             solutions++;
17             return;
18         }
19         
20         for (int i = 0; i < n; i++)
21         {
22             mark[row] = i;
23             if (check(mark, row))
24                 NQueen(mark, n, row + 1, solutions);
25         }
26     }
27     
28     bool check(vector<int> mark, int row)
29     {
30         for (int i = 0; i < row; i++)
31             if (mark[row] == mark[i] || abs(mark[row] - mark[i]) == (row - i))
32                 return false;
33         return true;
34     }