题解 | #走迷宫#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] str1 = br.readLine().split(" ");
        int n = Integer.parseInt(str1[0]);
        int m = Integer.parseInt(str1[1]);
        boolean[][] array = new boolean[n + 1][m + 1];
        String[] str2 = br.readLine().split(" ");
        int x1 = Integer.parseInt(str2[0]);
        int y1 = Integer.parseInt(str2[1]);
        int x2 = Integer.parseInt(str2[2]);
        int y2 = Integer.parseInt(str2[3]);
        for (int i = 1 ; i <= n; i++) {
            char[] chars = br.readLine().toCharArray();
            for (int j = 1; j <= m; j++) {
                array[i][j] = chars[j-1] == '.' ? true : false;
            }
        }
        Deque<int[]> queue = new ArrayDeque<>();
        //将起点加入队列并将array置为false
        queue.add(new int[] {x1, y1});
        array[x1][y1] = false;
        //记录步数
        int steps =  0;
        //图中每层未遍历的节点数
        int remain = 1;
        while (!queue.isEmpty()) {
            //每个点下层节点的个数
            int size = 0;

            while (remain > 0) {
                int[] position = queue.remove();//遍历
                int x = position[0];
                int y = position[1];
                remain --;
                //对周围的四个方位分别进行可达探测，从而得到遍历后的节点的下层节点
                if (y - 1 >= 1 && array[x][y - 1]) {
                    //到达指定位置
                    if (x == x2 && y-1 == y2) {
                        System.out.println(steps + 1);
                        return;
                    }

                    queue.add(new int[] {x, y - 1});
                    array[x][y - 1] = false;
                    size++;
                }
                if (y + 1 <= m && array[x][y + 1]) {
                    if (x == x2 && y + 1 == y2) {
                        System.out.println(steps + 1);
                        return;
                    }
                    queue.add(new int[] {x, y + 1});
                    array[x][y + 1] = false;
                    size++;
                }
                if (x - 1 >= 1 && array[x - 1][y]) {
                    if (x - 1 == x2 && y == y2) {
                        System.out.println(steps + 1);
                        return;
                    }
                    queue.add(new int[] {x - 1, y});
                    array[x - 1][y] = false;
                    size++;
                }
                if (x + 1 <= n && array[x + 1][y]) {
                    if (x + 1 == x2 && y == y2) {
                        System.out.println(steps + 1);
                        return;
                    }
                    queue.add(new int[] {x + 1, y});
                    array[x + 1][y] = false;
                    size++;
                }

            }
            remain = size;
            steps++;
        }
        System.out.println(-1);
    }
}