Description

Input

Output

Sample Input

Sample Output

去翻了點資料。。

題解在這裡

#include<cmath>
#include<ctime>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<complex>
#include<iostream>
#include<algorithm>
#include<iomanip>
#include<vector>
#include<string>
#include<bitset>
#include<queue>
#include<map>
#include<set>
using namespace std;

typedef long long ll;
typedef double db;

inline int read()
{
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch<='9'&&ch>='0'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
	return x*f;
}

void print(ll x)
{if(x<0)putchar('-'),x=-x;if(x>=10)print(x/10);putchar(x%10+'0');}

const int N=100100;

int n;

int last[N],a[N],s[N];

ll f[N];

vector<int>vect[N];

int head[N],tail[N];

inline ll cal(int x,int z)
{return f[x]+1ll*z*(s[x+1]-1)*(s[x+1]-1);}

inline db slope(int x,int y,int z)
{return 1.0*(cal(x,z)-cal(y,z))/(s[x+1]-s[y+1]);}

int main()
{
	n=read();
	register int i,j,l,r,mid;
	for(i=1;i<=n;++i)a[i]=read();
	for(i=1;i<=n;++i){s[i]=s[last[a[i]]]+1;last[a[i]]=i;}
	for(i=1;i<=n;++i)
	{
		vector<int> &vec=vect[a[i]];
		while(head[a[i]]+1<tail[a[i]]&&slope(vec[tail[a[i]]-1],vec[tail[a[i]]-2],a[i])<slope(i-1,vec[tail[a[i]]-1],a[i]))tail[a[i]]--,vec.pop_back();
		vec.push_back(i-1);tail[a[i]]++;
		if(tail[a[i]]==1)j=0;
		else if(slope(vec[tail[a[i]]-1],vec[tail[a[i]]-2],a[i])>2*a[i]*s[i])j=tail[a[i]]-1;
		else if(slope(vec[head[a[i]]],vec[head[a[i]]+1],a[i])<2*a[i]*s[i])j=head[a[i]];
		else 
		{
			l=1,r=tail[a[i]]-2;
			while(l<=r)
			{
				mid=(l+r)>>1;
				slope(vec[mid-1],vec[mid],a[i])>2*a[i]*s[i]?l=mid+1:r=mid-1;
			}
			j=l-1;
		}
		j=vec[j];
		f[i]=f[j]+1ll*(s[i]-s[j+1]+1)*(s[i]-s[j+1]+1)*a[i];
	}
	print(f[n]);puts("");
	return 0;
}
/*
5
2
2
5
2
3

21
*/