N皇后问题

N皇后问题

import java.util.*;

public class Solution {

    private int count;
    private LinkedList<int[]> result = new LinkedList<>();

    public int queen(int n){
        int[] columns = new int[n];
        recurse(n, 0, columns);
        return count;
    }

    private void recurse(int n, int row, int[] columns){
        if(row==n){
            count++;
            result.add(copyArray(columns));
            return;
        }
        for(int i=0;i<n;i++){
            columns[row] = i;
            int j;
            for(j=0;j<row;j++){
                if(columns[row]==columns[j] || (row-j)==Math.abs(columns[row]-columns[j])){
                    break;
                }
            }
            if(j==row){
                recurse(n, row+1, columns);
            }
        }
    }

    private int[] copyArray(int[] a){
        int[] b = new int[a.length];
        for(int i=0;i<a.length;i++){
            b[i] = a[i];
        }
        return b;
    }

    public static void main(String[] args) {
        Solution solution = new Solution();
        int n = solution.queen(8);
        System.out.println(n);
    }
}