求助，90分 #8TLE

#include<bits/stdc++.h>
using namespace std;
int m,n,p[1005][1005],l=0,r=0,mid;
bool flag=0,c[1005][1005]={0};
void dfs(int x,int y,int s){
	if(x==n||flag==1){
		flag=1;
		return;
	}
	if(x<=n&&c[x+1][y]==0&&p[x+1][y]<=s){
		c[x+1][y]=1;
		dfs(x+1,y,s);
	}
	if(x>2&&c[x-1][y]==0&&p[x-1][y]<=s){
		c[x-1][y]=1;
		dfs(x-1,y,s);
	}
	if(x!=1&&c[x][y+1]==0&&p[x][y+1]<=s&&y<m){
		c[x][y+1]=1;
		dfs(x,y+1,s);
	}
	if(x!=1&&c[x][y-1]==0&&p[x][y-1]<=s&&y>1){
		c[x][y-1]=1;
		dfs(x,y-1,s);
	}
	return;
}
bool judge(int x){
	for(int i=1;i<=m;i++){
		flag=0;
		memset(c,0,sizeof(c));
		dfs(1,i,x);
		if(flag==1)return 1;
	}
	return 0;
}
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			scanf("%d",&p[i][j]);
			r=max(r,p[i][j]);
		}
	}
	while(l+1<r){
		mid=(l+r)/2;
		if(judge(mid)==1)r=mid;
		else l=mid; 
	}
	cout<<r;
	return 0;
}