LeetCode N-Queens II

Follow up for N-Queens problem.

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

public class Solution {
    int result;  
    int[] A; 
    public int totalNQueens(int n) {
        A = new int[n];  
        nqueens(0, n);  
        return result;    
    }

     public void nqueens(int cur, int n){  
         if(cur==n) result++;  
         else {  
             for(int i=0;i<n;i++){  
                 A[cur] = i;  
                 if(valid(cur)){  
                     nqueens(cur+1, n);  
                 }  
             }  
         }  
     }  
     public boolean valid(int r){  
         for(int i=0;i<r;i++){  
             if(A[i]==A[r]|| Math.abs(A[i]-A[r])==r-i){  
                 return false;  
             }  
         }  
         return true;  
     }  
}