80分的悬线法，求助

#include <bits/stdc++.h>
using namespace std;
int l[2600][2600],r[2600][2600],u[2600][2600],a[2600][2600],f1[2600][2600],f2[2600][2600];
int n,m,ans;
int main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            cin>>a[i][j];
            l[i][j]=r[i][j]=j;
            u[i][j]=i;
            if(a[i][j])f1[i][j]=f2[i][j]=1;
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=2;j<=m;j++){
            if(a[i][j-1]==0)
            l[i][j]=l[i][j-1];
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=m-1;j>=1;j--){
            if(a[i][j+1]==0){
                r[i][j]=r[i][j+1];
            }
        }
    }
    for(int i=2;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(a[i-1][j]==0){
                u[i][j]=u[i-1][j];
            }
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(a[i][j]==0)continue;
            l[i][j]=max(l[i][j],l[i-1][j-1]);
            r[i][j]=min(r[i][j],r[i-1][j+1]);
            if(a[i-1][j-1]!=0){
                f1[i][j]+=f1[i-1][j-1];
            }
            if(a[i-1][j+1]!=0){
                f2[i][j]+=f2[i-1][j+1];
            }
            int lx=min(min(i-u[i][j]+1,j-l[i][j]+1),f1[i][j]);
            int ly=min(min(i-u[i][j]+1,r[i][j]-j+1),f2[i][j]);
            ans=max(ans,max(lx,ly));
        }
    }
    cout<<ans;
}