dfs算法

#include<cstdio>
char a1[110][110];
int n,m,map[110][110],vis[110][110],tmp;
int x[4]={0,0,1,-1},y[4]={-1,1,0,0};
void dfs(int x1,int y1){
	if(x1==n&&y1==m){
		tmp++;
		return;
	}
	for(int i=0;i<=3;i++){
		if(map[x1+x[i]][y1+y[i]]==1&&vis[x1+x[i]][y1+y[i]]==0){
			vis[x1+x[i]][y1+y[i]]=1;
			dfs(x1+x[i],y1+y[i]);
			vis[x1+x[i]][y1+y[i]]=0; 
		}
	}
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			scanf("%c",&a1[i][j]);
			if(a1[i][j]=='.'){
				map[i][j]=1;
			}else{
				map[i][j]=0;
			}
		}
	}
	dfs(n,m);
	if(tmp==0){
		printf("No");
	}else{
		printf("Yes");	
	}
}