随便给一串数列，求最长等差数列

3方水过，回头附n^2logn算法 （dp[i][j][k]=dp[i][k]+1)

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<cctype>
#include<iostream>
#include<functional>
#include<algorithm>
using namespace std;
#define MAXN (10000+10)
int n,a[MAXN];
int main()
{
	while (scanf("%d",&n)!=EOF)
	{
		for (int i=1;i<=n;i++) scanf("%d",&a[i]);
		sort(a+1,a+1+n);
		int ans=2;
		for (int i=1;i<=n;i++)
			for (int j=i+1;j<=n;j++)
			{
				int dd=a[j]-a[i],now=j,tot=2;
				for (int k=j+1;k<=n;k++)
				{
					if (a[k]-a[now]==dd)
					{
						tot++;
						now=k;
					}
				}
				ans=max(ans,tot);

			}
		cout<<ans<<endl;

	}



	return 0;
}