Acwing 795. 前缀和

#include <iostream>

using namespace std;

const int N = 100010;

int n, m;
int a[N], s[N];

int main()
{
    cin >> n >> m;
    
    for (int i = 1; i <= n; ++ i)
    {
        cin >> a[i];
        s[i] = s[i - 1] + a[i];
    }
    
    while (m --)
    {
        int l, r;
        cin >> l >> r;
        cout << s[r] - s[l - 1] << endl;
    }
    
    return 0;
}