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.."]
]

public class Solution {
List<String[]> result;  
    int[] A;  
    public List<String[]> solveNQueens(int n) {  
        result = new ArrayList<String[]>();  
        A = new int[n];  
        nqueens(0, n);  
        return result;  
    }  
    public void nqueens(int cur, int n){  
        if(cur==n) printres(n);  
        else {  
            for(int i=0;i<n;i++){  
                A[cur] = i;  
                if(valid(cur)){  
                    nqueens(cur+1, n);  
                }  
            }  
        }  
    }  
    public void printres(int n){  
        String[] tem = new String[n];  
        for(int i=0;i<n;i++){  
            StringBuffer sBuffer = new StringBuffer();  
            for(int j=0;j<n;j++){  
                if(j==A[i]) sBuffer.append('Q');  
                else sBuffer.append('.');  
            }  
            tem[i] = sBuffer.toString();  
        }  
        result.add(tem);  
    }  
    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;  
    }  
}