hdu 4745

直接在圈上写类似与lcs的dp就可以了

悲剧的是 （j+1）% n 直接写成了 j+1，死都找不到错

#pragma comment(linker, "/STACK:102400000,102400000")
#include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<stack>
#include<string>
#include<map>
#include<set>
#include<cmath>
#include<cassert>
#include<cstring>
#include<iomanip>
using namespace std;
#ifdef _WIN32
#define i64 __int64
#define out64 "%I64d\n"
#define in64 "%I64d"
#else
#define i64 long long
#define out64 "%lld\n"
#define in64 "%lld"
#endif
/************ for topcoder by zz1215 *******************/
#define foreach(c,itr)  for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)
#define FOR(i,a,b)      for( int i = (a) ; i <= (b) ; i ++)
#define FF(i,a)         for( int i = 0 ; i < (a) ; i ++)
#define FFD(i,a,b)      for( int i = (a) ; i >= (b) ; i --)
#define S64(a)          scanf(in64,&a)
#define SS(a)           scanf("%d",&a)
#define LL(a)           ((a)<<1)
#define RR(a)           (((a)<<1)+1)
#define pb              push_back
#define pf              push_front
#define X               first
#define Y               second
#define CL(Q)           while(!Q.empty())Q.pop()
#define MM(name,what)   memset(name,what,sizeof(name))
#define MC(a,b)         memcpy(a,b,sizeof(b))
#define MAX(a,b)        ((a)>(b)?(a):(b))
#define MIN(a,b)        ((a)<(b)?(a):(b))
#define read            freopen("in.txt","r",stdin)
#define write           freopen("out.txt","w",stdout)

const int inf = 0x3f3f3f3f;
const i64 inf64 = 0x3f3f3f3f3f3f3f3fLL;
const double oo = 10e9;
const double eps = 10e-9;
const double pi = acos(-1.0);
const int maxn = 1111;

int n;
int s[maxn];
int dp[maxn][maxn];

int start()
{
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<n;j++)
		{
			dp[i][j] = 0;
		}
	}

	for(int i=0;i<n;i++)
	{
		dp[i][i] = 1;
	}

	for(int j=0;j<n;j++)
	{
		if(s[j] == s[(j+1)%n])
		{
			dp[j][(j+1)%n] = 2;
		}
		else
		{
			dp[j][(j+1)%n] = 1;
		}
	}

	for(int i=2;i<n;i++)
	{
		for(int j=0;j<n;j++)
		{
			if(s[j] == s[(j+i)%n] )
			{
				dp[j][(j+i)%n] = dp[(j+1)%n][(j+i-1+n)%n] + 2;
			}
			else
			{
				dp[j][(j+i)%n] = max(dp[(j+1)%n][(j+i)%n],dp[j][(j+i-1+n)%n]);  //好吧，就是这写错了
			}
		}
	}

	int ans = 0;

	for(int i=0;i<n;i++)
	{
		ans = max(ans,dp[i][(i+n-2)%n]+1);
		ans = max(ans,dp[i][(i+n-1)%n]);
	}

	return ans;
}

int main()
{
	while(cin>>n)
	{
		if(n == 0) return 0;

		for(int i=0;i<n;i++)
		{
			SS(s[i]);
		}
		if(n==1) cout<<1<<endl;
		else cout<<start()<<endl;
	}
	return 0;
}