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 {
public List<String[]> solveNQueens(int n) {
List<String[]> result = new LinkedList<String[]>();
search(result,n,new ArrayList<Integer>(),1);
return result;
}
private boolean isValid(ArrayList<Integer> al) {
int column = al.get(al.size() - 1);
for (int i = 0; i < al.size() - 1; i++) {
if (column == al.get(i)
|| Math.abs(column - al.get(i)) == Math.abs(al.size()-1 - i)) {
return false;
}
}
return true;
}
private void search(List<String[]>result,int n, ArrayList<Integer> al, int col) {
if (col > n){
char []temp=new char[n];
Arrays.fill(temp, '.');
String []str=new String[n];
for(int i=0;i<al.size();i++){
StringBuilder sb=new StringBuilder(String.valueOf(temp));
sb.setCharAt(al.get(i), 'Q');
str[i]=sb.toString();
}
result.add(str);
}else {
for (int j = 0; j < n; j++) {
al.add(j);
if (isValid(al)) {
search(result,n, al, col + 1);
}
al.remove(al.size()-1);
}
}
}
public static void main(String []args){
Solution s=new Solution();
int n=8;
List<String []> result=s.solveNQueens(n);
for(String []str:result){
System.out.println(Arrays.toString(str));
}
System.out.println("\n"+result.size());
}
}原文地址：http://blog.csdn.net/mlweixiao/article/details/40984541
