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 {
int queenPosition[];
int N;
List<String[]>resultList;
StringBuilder line;
Set<Integer> getRemainingPosition(int index){
Set<Integer> result=new HashSet<Integer>();
int i,j;
for(i=0;i<N;i++){
result.add(i);
}
for(i=0;i<N;i++){
for(j=0;j<index;j++){
if((i==queenPosition[j])||(Math.abs(i-queenPosition[j])==Math.abs(index-j))){
result.remove(i);
break;
}
}
}
return result;
}
public void calNQueens(int index)
{
Set<Integer> remainingPosition=getRemainingPosition(index);
if(index+1==N){
for(Integer position:remainingPosition)
{
queenPosition[index]=position;
String []result=new String[N];
for(int i=0;i<N;i++)
{
line.setCharAt(queenPosition[i],'Q');
result[i]=line.toString();
line.setCharAt(queenPosition[i],'.');
}
resultList.add(result);
}
}
else
{
for(Integer position:remainingPosition)
{
queenPosition[index]=position;
calNQueens(index+1);
}
}
}
public List<String[]> solveNQueens(int n)
{
N=n;
resultList=new LinkedList<String[]>();
queenPosition=new int[N];
line=new StringBuilder(N);
for(int i=0;i<N;i++)
{
line.append(".");
}
calNQueens(0);
return resultList;
}
}原文地址：http://blog.csdn.net/jiewuyou/article/details/39154491
