AcWing 795. 前缀和

Posted 2022-02-09 MangataTS

题目连接

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

思路

前缀和板子，我们通过$pre[i]=pre[i-1]+a[i]$能维护a的前缀和

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define mod 1000000009
#define endl "\\n"
#define PII pair<int,int>
ll ksm(ll a,ll b) 
	ll ans = 1;
	for(;b;b>>=1LL) 
		if(b & 1) ans = ans * a % mod;
		a = a * a % mod;
	
	return ans;


ll lowbit(ll x)return -x & x;

const int N = 2e6+10;
ll n,m,a[N];

int main()

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