题解 | 区间和

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

int main() {
    int n, q;
    cin >> n >> q;
    vector<long long> arr(n + 1);
    for (int i = 1; i <= n; ++i)
        cin >> arr[i];
    // 构建前缀和数组
    vector<long long> p(n + 1);
    long long preSum = 0;
    for (int i = 1; i <= n; ++i) {
        preSum += arr[i];
        p[i] = preSum;
    }
    // 查询区间和
    for (int i = 0; i < q; ++i) {
        int l, r;
        cin >> l >> r;
        cout << p[r] - p[l - 1] << endl;
    }
    return 0;
}