1 #include<stdio.h>
 2 #include<string.h>
 3 #include<stdlib.h>
 4 #define maxn 100002
 5 int str[maxn<<1];
 6 int ra[maxn<<1];
 7 int min(int a,int b){
 8  return a<b?a:b;
 9 }
10 int manacher(int len){
11 
12     int mx=0,ce=0,ans=0;
13     memset(ra,0,sizeof(int)*(len+1));
14     for(int i=1;i<=len;i++){
15      if(mx>i)ra[i]=min(ra[ce*2-i],mx-i);
16      else  ra[i]=1;
17      while(str[i-ra[i]]==str[i+ra[i]]&&(str[i+ra[i]-2]==1||str[i+ra[i]-2]>=str[i+ra[i]])){
18         ra[i]++;
19       }
20      if(i+ra[i]>mx){
21          mx=i+ra[i];
22          ce=i;
23      }
24      if(ans<ra[i])ans=ra[i];
25     }
26     return ans;
27 }
28 
29 int main(){
30   int cas,n;
31  // freopen("test.in","r",stdin);
32  // system("call test.in");
33   scanf("%d",&cas);
34    str[0]=-1;
35   while(cas--){
36       scanf("%d",&n);
37       int len=(n<<1);
38       for(int i=2;i<=len;i+=2){
39            str[i-1]=1;
40       scanf("%d",&str[i]);
41     }
42        str[len+1]=1;
43     printf("%d\n",manacher(len+1)-1);
44   }
45 }