hdu4513(manacher)

#pragma comment(linker,"/STACK:1024000000,1024000000")
#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <limits.h>
#include <iostream>
#include <algorithm>
#include <queue>
#include <cstdlib>
#include <stack>
#include <vector>
#include <set>
#include <map>
#define LL long long
#define mod 1000000007
#define inf 0x3f3f3f3f
#define eps 1e-6
#define N 100010
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define PII pair<int,int>
using namespace std;
inline LL read()
{
    char ch=getchar();LL x=0,f=1;
    while(ch>‘9‘||ch<‘0‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch<=‘9‘&&ch>=‘0‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}
int p[N<<1],ans,len,num,mx,id;
int a[N],c[N<<1],n;
void build()
{
    n=read();
    for(int i=0;i<n;i++)a[i]=read();
    num=0;
    c[num++]=-1;c[num++]=inf;
    for(int i=0;i<n;i++)
    {
        c[num++]=a[i];
        c[num++]=inf;
    }
    c[num]=-2;
}
void manacher()
{
    ans=1;mx=0;
    memset(p,0,sizeof(p));
    for(int i=1;i<num;i++)
    {
        if(mx>i)p[i]=min(p[2*id-i],mx-i);
        else p[i]=1;
        while(c[i-p[i]]==c[i+p[i]]&&(c[i-p[i]]==inf||p[i]==1||c[i-p[i]]<=c[i-p[i]+2]))p[i]++;
        if(p[i]+i>mx)mx=p[i]+i,id=i;
        ans=max(ans,p[i]-1);
    }
}
int main()
{
    int T;
    T=read();
    while(T--)
    {
        build();
        manacher();
        printf("%d\n",ans);
    }
}