LeetCode N-Queens

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

For example,
There exist two distinct solutions to the 4-queens puzzle:

[
 [".Q..",  // Solution 1
  "...Q",
  "Q...",
  "..Q."],

 ["..Q.",  // Solution 2
  "Q...",
  "...Q",
  ".Q.."]
]

 1 public class Solution {
 2 List<String[]> result;  
 3     int[] A;  
 4     public List<String[]> solveNQueens(int n) {  
 5         result = new ArrayList<String[]>();  
 6         A = new int[n];  
 7         nqueens(0, n);  
 8         return result;  
 9     }  
10     public void nqueens(int cur, int n){  
11         if(cur==n) printres(n);  
12         else {  
13             for(int i=0;i<n;i++){  
14                 A[cur] = i;  
15                 if(valid(cur)){  
16                     nqueens(cur+1, n);  
17                 }  
18             }  
19         }  
20     }  
21     public void printres(int n){  
22         String[] tem = new String[n];  
23         for(int i=0;i<n;i++){  
24             StringBuffer sBuffer = new StringBuffer();  
25             for(int j=0;j<n;j++){  
26                 if(j==A[i]) sBuffer.append('Q');  
27                 else sBuffer.append('.');  
28             }  
29             tem[i] = sBuffer.toString();  
30         }  
31         result.add(tem);  
32     }  
33     public boolean valid(int r){  
34         for(int i=0;i<r;i++){  
35             if(A[i]==A[r]|| Math.abs(A[i]-A[r])==r-i){  
36                 return false;  
37             }  
38         }  
39         return true;  
40     }  
41 }