首页 > 其他分享> 文章详细

C. Almost Arithmetical Progression（DP）

2019-08-20 10:03:39 阅读：314 来源： 互联网

标签：... Progression sequence Almost int subsequence integer input DP

C. Almost Arithmetical Progression

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

Gena loves sequences of numbers. Recently, he has discovered a new type of sequences which he called an almost arithmetical progression. A sequence is an almost arithmetical progression, if its elements can be represented as:

a1 = p, where p is some integer;
ai = ai - 1 + ( - 1)i + 1·q (i > 1), where q is some integer.

Right now Gena has a piece of paper with sequence b, consisting of n integers. Help Gena, find there the longest subsequence of integers that is an almost arithmetical progression.

Sequence s1, s2, ..., sk is a subsequence of sequence b1, b2, ..., bn, if there is such increasing sequence of indexes i1, i2, ..., ik(1 ≤ i1 < i2 < ... < ik ≤ n), that bij = sj. In other words, sequence s can be obtained from b by crossing out some elements.

Input

The first line contains integer n (1 ≤ n ≤ 4000). The next line contains n integers b1, b2, ..., bn (1 ≤ bi ≤ 106).

Output

Print a single integer — the length of the required longest subsequence.

Examples

input

Copy

2
3 5

output

Copy

input

Copy

4
10 20 10 30

output

Copy

Note

In the first test the sequence actually is the suitable subsequence.

In the second test the following subsequence fits: 10, 20, 10.

【思路】

dp[i][j] i表示当前数的位置，j表示前面的数。

AC代码：

#include <iostream>
#include <cstring>
using namespace std;
int b[4005];
int dp[4005][4005];
int N;
int main()
{
    cin>>N;
    for(int i=1;i<=N;i++)
    {
        cin>>b[i];
    }
    memset(dp,0,sizeof(dp));
    int res=0;
    for(int i=1;i<=N;i++)
    {
        int t=0;
        for(int j=0;j<i;j++)
        {
            dp[i][j]=dp[j][t]+1;
            if(b[i]==b[j])
                t=j;
            res=max(res,dp[i][j]);
        }
    }
    cout<<res<<endl;
    return 0;
}

标签：...,Progression,sequence,Almost,int,subsequence,integer,input,DP
来源： https://blog.csdn.net/qq_43956340/article/details/99819234

本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享；
2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关；
3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关；
4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除；
5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。

ICode9

C. Almost Arithmetical Progression（DP）