N皇后问题---采用深度优先搜索算法求解

一.问题描述

     将棋子放在N*N的棋盘中，要求两个棋子不能在同一列，同一行及同一斜对角线上

二.代码

  

import java.util.HashMap;
import java.util.Map;

public class Queen {
    private int count = 0;

    private Integer n = 0;

    //棋子已有的坐标
    private Map location = new HashMap<>();
    private Map reverseLocation = new HashMap<>();  //坐标反转
    private static final Integer UNCAPTURED = 0;

    private static final Integer CAPTURED = 1;


    private int[][] chessboard;

    Queen(int n) {
        this.n = n;
        this.chessboard = new int[n][n];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                chessboard[i][j] = UNCAPTURED;
            }
        }
    }

    private void dfs(int depth) {
        if (depth == n) {
            System.out.println("resolution :"+count+" start *****************");
            for (Map.Entry entry : location.entrySet()) {
                System.out.println("x is:"+entry.getKey()+";y is:"+entry.getValue());
            }
            System.out.println("resoluction :"+count+" end ********");
            count++;
            return;
        }
        for (int i = 0; i < n; i++) {
            if (isSatisfied(depth, i)) {
                location.put(depth, i);
                reverseLocation.put(i, depth);
                dfs(depth + 1);
                location.remove(depth);
                reverseLocation.remove(i);
            }
        }
    }

    public int getCount() {
        dfs(0);
        return count;
    }

    private boolean isSatisfied(Integer i, Integer j) {
        //在同一行或同一列
        if (location.containsKey(i) || reverseLocation.containsKey(j)) {
            return false;
        }

        for (Map.Entry entry : location.entrySet()) {
            //在斜对角线上
            if (Math.abs(entry.getKey() - i) == Math.abs(entry.getValue() - j)) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        Queen queen = new Queen(4);
        System.out.println(queen.getCount());
    }


}