模板 前缀和 NC

例题

#include <bits/stdc++.h>
#define endl '\n'
#define int long long 
#define INF 0x3f3f3f3f3f
const int N = 1000010;
using namespace std;
int arr[N],pre[N];

signed main()
{
	std::ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	int n,q;
	int l,r;
	cin>>n>>q;
	for(int i = 1; i<= n; i++){
		cin>>arr[i];
        //记录前缀和
		pre[i] = pre[i-1] + arr[i];
	}
	while(q--){
		cin>>l>>r;
		cout<<pre[r] - pre[l-1]<<endl;
	}
	return 0;
}