C++ 代码

// 前缀和的公式 s[i] = a[1]+...a[i]; a[i]=s[i]-s[i-1], s[i]=s[i-1]+a[i]; s[0]=0; a[1]=s[1]-s[0]=s[1]=a[1]

#include <iostream>
using namespace std;

const int N = 1e5+10;

int s[N];

int main() {

    int n, m;
    cin >> n >> m;

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

    return 0;
}