C++(clang++11) 解法, 执行用时: 52ms, 内存消耗: 3536K, 提交时间: 2021-02-13 09:32:05

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<stack>
#define in(a) a=read()
#define MAXN 200020
#define REP(i,k,n) for(long long i=k;i<=n;i++)
using namespace std;
inline long long read()
{
	long long x=0,f=1;
	char ch=getchar();
	for(;!isdigit(ch);ch=getchar())
	if(ch=='-')
	f=-1;
	for(;isdigit(ch);ch=getchar())
	x=x*10+ch-'0';
	return x*f; 
}
long long n;
long long ans;
long long a[MAXN],s[MAXN];
inline bool check(long long i,long long k)
{
	long long sum=s[i+k-1]-s[i-1];
	long long loc=i+k-1;
	long long left=0,right=n;
	while(right-left>1)
	{
		long long mid=(right+left)/2;
		if(s[loc+mid]-s[loc]<sum&&s[i+n-1]-s[loc+mid]<sum)
		return 0;
		if(s[loc+mid]-s[loc]<sum)
		left=mid;
		if(s[i+n-1]-s[loc+mid]<sum)
		right=mid;
		if(s[loc+mid]-s[loc]>=sum&&s[i+n-1]-s[loc+mid]>=sum)
		return 1;
	}
	return 0;
}

int main()
{
	in(n);
   REP(i,1,n)
   {
   	in(a[i]);
   	a[i+n]=a[i];
   	s[i]=s[i-1]+a[i];
   }
   REP(i,1,n)
   s[n+i]=s[i+n-1]+a[i+n];
   REP(i,1,n)
   {
   	long long left=0,right=n;
   	while(right-left>1)
   	{
   		long long mid=(left+right)/2;
   		if(check(i,mid))
   		left=mid;
   		else
   		right=mid;
	   }
	   ans=max(s[i+left-1]-s[i-1],ans);
   }
   cout<<ans;
   return 0;
}