前缀和

//洛谷p8218求区间和

#include<iostream>
using namespace  std;
const int N = 100010;
int n;
int m;
int a[N], s[N];


int main() {

	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		s[i] = s[i - 1] + a[i];
   }
	cin >> m;
	while (m--) {
		int l, r; 
		cin >> l >> r;
		cout << s[r] - s[l - 1]<<endl;
	}

}

//洛谷p1719最大加权矩形(二维)

#include<iostream>
using namespace std;

const int N = 10010;
int a[N][N];
int s[N][N];

int main() {
    int n;
    cin >> n;

    // 读取矩阵并计算前缀和
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; 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 tmp = a[1][1];  // 将 tmp 初始化为矩阵的左上角元素

    // 使用四重循环找到最大子矩阵和
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            for (int k = i; k <= n; k++) {
                for (int l = j; l <= n; l++) {
                    int cur = s[k][l] - s[k][j - 1] - s[i - 1][l] + s[i - 1][j - 1];
                    if (cur > tmp) {
                        tmp = cur;
                    }
                }
            }
        }
    }

    cout << tmp << endl;  // 输出最大子矩阵和
    return 0;
}