AcWing 795. 前缀和

题目连接

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

思路

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

#include
using namespace std;
#define ll long long
#define mod 1000000009
#define endl "\n"
#define PII pair
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 >a[i];
		a[i] += a[i-1];
	}
	int l,r;
	while(m--) {
		cin>>l>>r;
		cout