CUBE-182: Maximum Submatrix Sum

#include <bits/stdc++.h>
using namespace std;
const long long INF=2e18;
vector <vector<long long>> qs(1001,vector<long long>(1001,0));
int main(){
    int n,h,w;
    long long mx=-INF;

    scanf("%d%d%d",&n,&h,&w);

    for(int i=1;i<=n;i++){
        scanf("%lld",&qs[i][0]);
    }
    for(int i=1;i<=n;i++){
        scanf("%lld",&qs[0][i]);
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(i==1&&j==1) qs[i][j] = qs[i][0]+qs[0][j];
            else if(i==1) qs[i][j] = (qs[i][0]+qs[0][j]) + qs[i][j-1];
            else if(j==1) qs[i][j] = (qs[i][0]+qs[0][j]) + qs[i-1][j];
            else  qs[i][j] = (qs[i][0]+qs[0][j]) + qs[i-1][j] + qs[i][j-1] - qs[i-1][j-1];
            if(i>=h && j>=w){
                if(i-h<=0 && j-w<=0) mx=max(mx, qs[i][j]);
                else if(i-h<=0) mx=max(mx, qs[i][j] - qs[i][j-w] );
                else if(j-w<=0) mx=max(mx, qs[i][j] - qs[i-h][j] );
                else mx = max(mx, qs[i][j] - qs[i-h][j] - qs[i][j-w] + qs[i-h][j-w] );
            }
        }
    }
    printf("%lld",mx);

    return 0;
}