基础前缀和

https://www.acwing.com/problem/content/797/

#include<cstring>
#include<algorithm>
#include<cstdio>
#include<iostream>
using namespace std;
const int N = 1e5+5;
int n,m,l,r;
int a[N],s[N];
int main()
{
	cin >> n >> m;
	for(int i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		s[i]=s[i-1]+a[i];
	}
	while(m--)
	{
		scanf("%d%d",&l,&r);
		printf("%d\n",s[r]-s[l-1]);
	}
	return 0;
}