50pts求条

#include<bits/stdc++.h>
using namespace std;
int x[]={1,-1,0,0};
int y[]={0,0,1,-1};
int f=0;
int n,m;
char a[105][105];
void dfs(int xx,int yy){
    if(xx==n&&yy==m){
        f=1;
        return ;
    }
    for(int i=0;i<4;i++){
        if(xx+x[i]<=n&&xx+x[i]>=1&&yy+y[i]>=1&&yy+y[i]<=m&&a[xx+x[i]][yy+y[i]]=='.'){
            a[xx+x[i]][yy+y[i]]='#';
            dfs(xx+x[i],yy+y[i]);       
            if(f){
                return ;
            }
            a[xx+x[i]][yy+y[i]]='.';
        }
    }   
}
int main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        for(int t=1;t<=m;t++){
            cin>>a[i][t];
        }
    }
    dfs(1,1);
    if(f)
    cout<<"Yes";
    else cout<<"No";

    return 0;
}