5wa了

92

代码如下：

#include <iostream>
using namespace std;
const int NR=2501;
int n,m,i,j,a[NR][NR],leftt[NR][NR],up[NR][NR],f[NR][NR],answer,ans,ans1,ans2;
void fan()
{
    for(i=1;i<=(n+1)/2;i++)
        for(j=1;j<=(m+1)/2;j++)
        {
            swap(a[i][j],a[i][m-j+1]);
        }
}
int solve()
{
    ans=-1;
    //leftt
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        {
            if(a[i][j]==0)
                leftt[i][j]=leftt[i][j-1]+1;
            else
                leftt[i][j]=0;
        }
    //up
    for(j=1;j<=m;j++)
        for(i=1;i<=n;i++)
        {
            if(a[i][j]==0)
                up[i][j]=up[i-1][j]+1;
            else
                up[i][j]=0;
        }
    //f
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        {
            if(a[i][j]==0)
                f[i][j]=0;
            else
            {
                f[i][j]=min(up[i-1][j],min(leftt[i][j-1],f[i-1][j-1]))+1;
            }
            ans=max(f[i][j],ans);
        }
        return ans;
}
int main()
{
    ans=-1;
    //input
    cin>>n>>m;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=m;j++)
            cin>>a[i][j];
    }
    ans1=solve();
    fan();
    ans2=solve();
    cout<<max(ans1,ans2)<<endl; 
    return 0;
}

分两次DP，分别取左下和右下开吃。

蒟蒻求调！！！