经典算法之走迷宫

问题描述:

...11111111111111111111111111111
11.111111........1111111111.1111
11.111111..111.11111111.....1111
11.11111111111.1111111111.111111
11.111111.................111111
11.111111.11111111111.11111.1111
11.111111.11111111111.11111..111
11..........111111111.11111.1111
11111.111111111111111.11....1111
11111.111111111111111.11.11.1111
11111.111111111111111.11.11.1111
111...111111111111111.11.11.1111
111.11111111111111111....11.1111
111.11111111111111111111111.1111
111.1111.111111111111111......11
111.1111.......111111111.1111.11
111.1111.11111.111111111.1111.11
111......11111.111111111.1111111
11111111111111.111111111.111...1
11111111111111...............1.1
111111111111111111111111111111..


如上图的迷宫，入口，出口分别：左上角，右下角
"1"是墙壁，"."是通路
求最短需要走多少步？

解题思路:

用*表示已走的路,用广度优先搜索求最短路径.

代码实现:

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Main {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		
		String[] ss = input.nextLine().trim().split(" +");
		int n = Integer.parseInt(ss[0]);  //数组的第一部分为迷宫的长
		int m = Integer.parseInt(ss[1]);  //数组的第二部分为迷宫的宽
		
		char[][] data = new char[n][];
		for (int i = 0; i < n; i++) {
			data[i] = input.nextLine().trim().toCharArray();   //正文部分为迷宫的内部构造
		}
		
		Set<String> set = new HashSet<>();   //set用来保存走的路径
		set.add("0,0");  //将迷宫的左上角(0, 0)设为起点, 右下角设为终点
		System.out.println(fun(data, set, n-1 + "," +(m -1)));
	}

	public static int fun(char[][] data, Set<String> from, String goal) {
		if (from.contains(goal)) return 0;    //起点与终点重合,需要0步完成
		Set<String> set = new HashSet<>();     //from相邻的未访问的点
		
		for (Object obj : from) {
			String[] ss = ((String) obj).split(",");
			int y = Integer.parseInt(ss[0]);
			int x = Integer.parseInt(ss[1]);
			
			if (y > 0 && data[y - 1][x] == '.') {
				data[y - 1][x] = '*';
				set.add(y - 1 + "," + x);
			}
			if (y < data.length - 1 && data[y + 1][x] == '.') {
				data[y + 1][x] = '*';
				set.add(y + 1 + "," + x);
			}
			if (y > 0 && data[y][x - 1] == '.') {
				data[y][x - 1] = '*';
				set.add(y + "," + (x - 1));
			}
			if (y < data.length - 1 && data[y][x + 1] == '.') {
				data[y][x + 1] = '*';
				set.add(y + "," + (x + 1));
			}
		}
			
		if (set.isEmpty()) return -1;
		int r = fun(data, set, goal);    //分层遍历 广度优先遍历
		if (r < 0) return -1;   //找不到出口 返回-1
		return r + 1;
	}
}

github:https://github.com/striner/javaCode/blob/master/maze