erwei

二维前缀和

1002. 二哥种花生

https://acm.sjtu.edu.cn/OnlineJudge/problem/1002

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e3 + 5;
int l,w;
int a[maxn][maxn],s[maxn][maxn];
int main(){
    //freopen("in","r",stdin);
    ios::sync_with_stdio(0);
    cin >> l >> w;
    for(int i = 1; i <= l; i++){
        for(int j = 1; j <= w; j++){
            cin >> a[i][j];
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + a[i][j];
        }
    }
    int ans = 0;
    int a,b;
    cin >> a >> b;
    for(int x1 = 1; x1 <= l; x1++){
        for(int y1 = 1; y1 <= w; y1++){
           int x2 = x1 + a - 1,y2 = y1 + b - 1;
           if(x2 <= l && y2 <= w){
               int t = s[x2][y2] - s[x1 - 1][y2] - s[x2][y1 - 1] + s[x1 - 1][y1 - 1];
               ans = max(ans,t);
           }
        }
    }
    cout << ans;
    return 0;
}

二维差分