AcWing 796. 子矩阵的和

#include <iostream>
using namespace std;
const int N = 1010;
int sum[N][N];
int main (){
    int a[N][N],n,m,q;
    long long sum[N][N];
    cin >> n >> m >> q;
    // for(int i = 0; i <= n; i++ ) sum[i][0] =0;
    // for(int j = 0; j <= m; j++ ) sum[0][j] =0;
    for(int i = 1; i <= n; i++ ){
        for(int j = 1; j <= m; j++){
            cin >> a[i][j];
            sum[i][j] = sum[i][j-1] + sum[i-1][j] - sum[i-1][j-1] + a[i][j];
        }
    }
    while(q--){
        int x1,y1,x2,y2;
        cin >> x1 >> y1 >> x2 >> y2;
        cout << sum[x2][y2] - sum[x1-1][y2] -sum[x2][y1-1] + sum[x1-1][y1-1] << endl;
    }
    return 0;
}