求助，环形最大子段和

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int N=1000006;
ll n,a[N*2],f[N*2],sum,ans;
deque<pair<int,int> >q;
int main(){
	freopen("subsegment.in","r",stdin);
	freopen("subsegment.out","w",stdout);
	cin>>n;
	for (int i=1;i<=n;i++)
		cin>>a[i],a[i+n]=a[i];
	n*=2;
	for (int i=1;i<=n;i++){
		while(!q.empty()&&q.front().first<=i-(n/2)) sum-=q.front().second,q.pop_front();
		if (sum+a[i]<=0){
			f[i]=0;
			sum=0;
			q.clear();
		}
		else{
			sum+=a[i];
			q.push_back(make_pair(i,a[i]));
			f[i]=sum;
		}
	}
	for (int i=1;i<=n;i++)
		ans=max(f[i],ans);
	cout<<ans<<endl;
	return 0;
}