```cpp
#include<iostream>
#include<algorithm>
using namespace std;int n,m,ans,a,f[10000][10000];int main(){cin>>n>>m;for(int i=1;i<=n;i++)for(int j=1;j<=m;j++){cin>>a;if(a==1)f[i][j]=min(min(f[i-1][j],f[i][j-1]),f[i-1][j-1])+1,ans=max(ans,f[i][j]);}cout<<ans;return 0;}
```
by a66666 @ 2018-06-24 19:31:32
@[SSerxhs](/space/show?uid=29826) 我也0msAC用前缀和
by Owen_codeisking @ 2018-07-08 08:29:41
泥萌让我这种只会O(n^4)的蒟蒻怎么活啊
by FCBM71 @ 2018-08-02 10:21:01