30分，求助大佬

#include<iostream>
#include<cstdio>
#define size 2505
using namespace std;
int n,m;
bool data[size][size];
int sum1[size][size],sum2[size][size],maxlen;
short line1[size][size],line2[size][size];
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            scanf("%d",&data[i][j]);
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            sum1[i][j]=sum1[i][j-1]+data[i][j];
            sum2[i][j]=sum2[i-1][j]+sum1[i][j];
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(data[i][j]){
                line1[i][j]=line1[i-1][j-1]+1;
            }
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(data[i][j]){
                line1[i][j]=line1[i-1][j+1]+1;
            }
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(line1[i][j]>maxlen){
                if(line1[i][j]==sum2[i][j]-sum2[i-line1[i][j]][j]-sum2[i][j-line1[i][j]]+sum2[i-line1[i][j]][j-line1[i][j]]){
                    maxlen=line1[i][j];
                }
            }
        }
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(line2[i][j]>maxlen){
                if(line2[i][j]==sum2[i][j]-sum2[i-line2[i][j]][j]-sum2[i][j-line2[i][j]]+sum2[i-line2[i][j]][j-line2[i][j]]){
                    maxlen=line2[i][j];
                }
            }
        }
    }
    printf("%d",maxlen);
    return 0;
}