解析+代码的题解

直接套公式！！
前缀和公式：sum[i] = sum[i-1] + a[i]

#include <bits/stdc++.h>
using namespace std;
int sum[100005];
int main()
{
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        int x;
        cin >> x;
        sum[i] = sum[i - 1] + x;
    }
    for (int i = 1; i <= m; i++)
    {
        int l, r;
        cin >> l >> r;
        cout << sum[r] - sum[l - 1] << endl;
    }
    return 0;
}