信息学奥赛一本通T1252-走迷宫

#include <bits/stdc++.h>
#define x first
#define y second
using namespace std;
typedef pair<int,int> pii;
const int dx[4] = {1,0,-1,0};
const int dy[4] = {0,-1,0,1};
const int N = 50;
char g[N][N];
bool st[N][N];
int d[N][N];
int n, m;
void bfs()
{
    queue<pii> q;
    q.push({0,0});
    st[0][0] = true;
    d[0][0] = 1;
    while(q.size())
    {
        pii t = q.front();
        q.pop();
        for(int k = 0; k < 4; k++)
        {
            int nx = t.x + dx[k], ny = t.y + dy[k];
            if(nx >= 0 && nx < n && ny >= 0 && ny < m)
            {
                if(!st[nx][ny] && g[nx][ny] == '.')
                {
                    st[nx][ny] = true;
                    d[nx][ny] = d[t.x][t.y] + 1;
                    q.push({nx,ny});
                }
            }
        }
    }
}
int main()
{
    cin >> n >> m;
    for(int i = 0; i < n; i++) cin >> g[i];
    bfs();
    cout << d[n-1][m-1] << endl;
    return 0;
}