题面
代码：

#include <bits/stdc++.h>
	using namespace std;
	
	int sx,sy,ex,ey,minn,apple;
	char c[805][805];
	int n,m;
	int tot,bzx[805],bzy[805];
	int dx[5]={0,0,1,0,-1};
	int dy[5]={0,1,0,-1,0};
	int ansa[805][805];
	
	bool vis[805][805];
	
	struct node{
		int x,y,step;
	};
	
	void banana()
	{
		queue<node>q;
		q.push((node){sx,sy,0});
		while(!q.empty()){
			node now=q.front();
			q.pop();
			if(now.x<1||now.y<1||now.x>n||now.y>m) continue;
			if(c[now.x][now.y]=='1'||c[now.x][now.y]=='3') continue;
			if(vis[now.x][now.y]==1) continue;
			vis[now.x][now.y]=1;
			ansa[now.x][now.y]=now.step;
			for(int i=1;i<=4;i++){
				q.push((node){now.x+dx[i],now.y+dy[i],now.step+1});
			}
		}
	}
	
	void china()
	{
		memset(vis,0,sizeof(vis));
		queue<node>q;
		q.push((node){ex,ey,1});
		while(!q.empty()){
			node now=q.front();
			q.pop();
			if(now.x<1||now.y<1||now.x>n||now.y>m) continue;
			if(c[now.x][now.y]=='1') continue;
			if(vis[now.x][now.y]==1) continue;
			vis[now.x][now.y]=1;
			ansa[now.x][now.y]+=now.step;
			for(int i=1;i<=4;i++){
				q.push((node){now.x+dx[i],now.y+dy[i],now.step+1});
			}
		}
	}
	
	signed main()
	{
		ios::sync_with_stdio();
		cin.tie(0);
		cout.tie(0);
		cin>>n>>m;
		for(int i=1;i<=n;i++)
		{
			for(int j=1;j<=m;j++)
			{
				cin>>c[i][j];
				if(c[i][j]=='3') 
				{
					ex=i;
					ey=j;
				}
				if(c[i][j]=='2')
				{
					sx=i;
					sy=j;
				}
				if(c[i][j]=='4')
				{
					bzx[++tot]=i;
					bzy[tot]=j;
				}
			}
		}
		banana();
		china();
		
		
		
		apple=805*805;	
		for(int i=1;i<=tot;i++){
			if(!vis[bzx[i]][bzy[i]]) continue;
			apple=min(apple,ansa[bzx[i]][bzy[i]]-1);
	//		cout<<ansa[bzx[i]][bzy[i]]<<"\n";
		}
		cout<<apple;
		
		return 0;
	}