子矩阵的和

输入一个 n行 m 列的整数矩阵，再输入 q 个询问，每个询问包含四个整数 x1,y1,x2,y2x1,y1,x2,y2，表示一个子矩阵的左上角坐标和右下角坐标。

输出子矩阵中所有数的和。

#include <iostream>
#include <cstdio>
using namespace std;
const int N = 1005;
int n, m, q;
int a[N][N], s[N][N];

int main() {
    cin >> n >> m >> q;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j ++) {
            cin >> a[i][j];
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + a[i][j];
        }
    }
    
    while (q--) {
        int x1, y1, x2, y2;
        cin >> x1 >> y1 >> x2 >> y2;
        cout << (s[x2][y2] - s[x2][y1 - 1] - s[x1 - 1][y2] + s[x1 - 1][y1 - 1]) << endl;
    }
    return 0;
}