//Name:Lazy_doghead
#include<bits/stdc++.h>
using namespace std;
bool op[31][31],ot;
char a[31][31];
void ptdfs(int dx,int dy,int k,int o){
	if(a[k][o]=='#')return;
	op[k][o]=true;
	if(k==dx&&o==dx){
		ot=true;
        return;
	}
	if(k-1>0&&!(op[k-1][o]))ptdfs(dx,dy,k-1,o);
	if(k+1<=dx&&!(op[k+1][o]))ptdfs(dx,dy,k+1,o);
	if(o-1>0&&!(op[k][o-1]))ptdfs(dx,dy,k,o-1);
	if(o+1<=dy&&!(op[k][o+1]))ptdfs(dx,dy,k,o+1);
	op[k][o]=false;
	return;
}
void ys(){
	int n,m,i,j,t;
	cin>>n>>m;
	for(i=1;i<=n;i++){
		for(j=1;j<=m;j++)cin>>a[i][j];
	}
	ptdfs(n,m,1,1);
	if(ot)cout<<"Yes";
	else cout<<"No";
}
int main(){
	ys();
	return 0;
}

调了半天了,悬赏一关