http://noi.openjudge.cn/ch0205/2753/ 实在不知道怎么做了

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#define maxn 41
using namespace std;

struct node {
	int x;
	int y;
};
queue<node> q;
char a[maxn][maxn];
int book[maxn][maxn];
int dis[maxn][maxn];
int r, c;
int mi = 1000;
int _next[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {-1, 0}};

int bfs() {
	while (!q.empty()) {
		node z = q.front();
		if (book[z.x][z.y] == 2) {
			return dis[z.x][z.y];
		}
		book[z.x][z.y] = 1;
		for (int i = 0 ; i < 4 ; i++) {
			int tx = z.x + _next[i][0];
			int ty = z.y + _next[i][1];
			if (book[tx][ty] != 1) {
				dis[tx][ty] = dis[z.x][z.y] + 1;
				q.push((node) {
					tx, ty
				});
			}
		}
		q.pop();
	}
	return 0;
}
int main() {
	cin >> r >> c;
	for (int i = 0; i <= r + 1; i++) {
		for (int j = 0 ; j <= c + 1; j++) {
			a[i][j] = '#';
			dis[i][j] = 0;
			book[i][j] = 1;
		}
	}
	for (int i = 1 ; i <= r; i++) {
		for (int j = 1; j <= c ; j++) {
			cin >> a[i][j];
			if (a[i][j] == '.') {
				book[i][j] = 0;
			}
		}
	}
	q.push((node) {
		1, 1
	});
	book[r][c] = 2;
//	for (int i = 1; i <= r; i++) {
//		for (int j = 1; j <= c; j++) {
//			cout << book[i][j] << " ";
//		}
//		cout << endl;
//	}
	dis[1][1] = 1;
	cout << bfs() << endl;
	return 0;
}