#include<bits/stdc++.h> using namespace std; typedef long long ll; ll a[200010],n,ans1=1,ans2=1,tong[2000010]; void FindAns(){ int l=1,r=n; while(l<=r){ if(a[l]==a[r]){ l++;r--; }else{ ans1=a[l]; ans2=a[r]; return; } } } bool check(int ans){ int l=1,r=n; while(l<=r){ if(a[l]==a[r]){ l++;r--; }else if(a[l]!=a[r]){ if(a[l]==ans){ l++; }else if(a[r]==ans){ r--; }else{ return 0; } } } return 1; } bool hw(){ int l=1,r=n; while(l<=r){ if(a[l]==a[r]){ l++;r--; }else{ return 0; } } return 1; } int main(){ ll t; cin>>t; while(t--){ ans1=ans2=1; cin>>n; for(ll i=1;i<=n;i++){ cin>>a[i]; tong[a[i]]=1; } if(hw()){ int sum=0; for(int i=1;i<=200010;i++){ if(tong[i]==1){ sum++; } } cout<<sum<<endl; for(int i=1;i<=200010;i++){ if(tong[i]==1){ cout<<i<<" "; } } cout<<endl; continue; } FindAns(); if(ans1!=ans2){ if(check(ans1)&&check(ans2)){ cout<<2<<endl; cout<<ans1<<" "<<ans2<<endl; }else if(check(ans1)){ cout<<1<<endl; cout<<ans1<<endl; }else if(check(ans2)){ cout<<1<<endl; cout<<ans2<<endl; }else{ cout<<0<<endl<<endl; } }else{ if(check(ans2)){ cout<<1<<endl; cout<<ans2<<endl; }else{ cout<<0<<endl<<endl; } } } return 0; }