前缀和应该也是体现了递归的思想吧

#include <iostream>

using namespace std;

const int N = 100010;
int a[N], b[N];

int main()
{
    int m, n, l, r;
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i ++ )  cin >> b[i];
    for(int i = 1; i <= n; i ++ )
        a[i] = a[i - 1] + b[i];
    while(m -- )
    {
        scanf("%d%d", &l, &r);
        printf("%d\n", a[r] - a[l - 1]);
    }

}