@rensiwei 求调

#include<bits/stdc++.h>
using namespace std;
int n,m;
char a[105][105];
int f[105][105];
int fy[4]={-1,1,0,0};
int fx[4]={0,0,1,-1};
int dfs(int x,int y){
	for(int i=0;i<4;i++){
		int dx=x+fx[i];
		int dy=y+fy[i];
		if(dx>=1&&dx<=n&&dy>=1&&dy<=m&&!f[dx][dy]&&a[dx][dy]=='.'){
			if(dx==n&&dy==m){
				cout<<"Yes";
				return 0;
			}
			f[dx][dy]=1;
			a[dx][dy]='#';
			dfs(dx,dy);
		}
	}
}
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>a[i][j];
		}
	}
	if(!dfs(1,1)){
		cout<<"No";
	}

	return 0;                       
}