P5459 [BJOI2016] 回转寿司

#include <bits/stdc++.h>
using namespace std;
long long a[100005];
long long sum[100005];
long long cnt;
int main(){
	long long n,l,r;
	cin >> n >> l >> r;
	for(int i=1;i<=n;i++){
		cin >> a[i];
		sum[i]=sum[i-1]+a[i];
	}
	for(int i=1;i<=n;i++){
		long long maxn=0,minn=n+1;
		long long L=i,R=n;
		if(sum[1]>r){
			continue;
		}
		while(L<=R){
			int mid=(L+R)/2;
			if(sum[mid]-sum[i-1]>=l){
				R=mid-1;
				minn=mid;
			}else{
				L=mid+1;
			}
		}
		L=i,R=n;
		while(L<=R){
			int mid=(L+R)/2;
			if(sum[mid]-sum[i-1]<=r){
				L=mid+1;
				maxn=mid;
			}else{
				R=mid-1;
			}
		}
		cnt+=max(maxn-minn+1,0ll);
	}
	cout << cnt;
	return 0;
}