题解 | 【模板】前缀和

#include <iostream>
#include <vector>
using namespace std;

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

    vector<long long> a(n + 1), sum(n + 1, 0); // 下标从1开始，sum[0] = 0

    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
        sum[i] = sum[i - 1] + a[i];
    }

    while (m--) {
        int l, r;
        cin >> l >> r;
        cout << sum[r] - sum[l - 1] << '\n';
    }

    return 0;
}