Code:

#include<bits/stdc++.h>
using namespace std;
#define map Map
int n, m;
int map[57][57];
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
void init() {
	char c;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			cin >> c;
			if (c == 'X')map[i][j] = 1;
		}
	}
}
void dfs(int x, int y) {
	map[x][y] = 2;
	for (int i = 0; i < 4; i++) {
		if (map[x + dx[i]][y + dy[i]] == 1) {
			dfs(x + dx[i], y + dy[i]);
		}
	}
}
struct node {
	int x, y;
};
node pot1[2500], pot2[2500];
int p1, p2;
void savepot() {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			if (map[i][j] == 2) {
				pot1[p1] = { i,j };
				p1++;
			}
			else if (map[i][j] == 1) {
				pot2[p2] = { i,j };
				p2++;
			}
		}
	}
}
int mht() {
	int min0 = 101, mht0;
	for (int i = 0; i < p1; i++) {
		for (int j = 0; j < p2; j++) {
			mht0 = abs(pot1[i].x - pot2[j].x) + abs(pot1[i].y - pot2[j].y) - 1;
			min0 = min(mht0, min0);
		}
	}
	return min0;
}
node first;
void findfirst() {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			if (map[i][j] == 1) {
				first = { i,j };
				return;
			}
		}
	}
}
int main() {
	cin >> n >> m;
	init();
	findfirst();
	dfs(first.x, first.y);
	savepot();
	int ans = mht();
	cout << ans;
	return 0;
}

AC合格证：