codeforces - phoenix and beauty

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fast()(ios_base::sync_with_stdio(0),cin.tie(NULL));
int main()
{
    ll t ;
    cin>> t;
    while(t--)
    {
        ll n, k;
        cin>>n>>k;
        set<ll>s;
        for(ll i = 0; i<n; i++)
        {
            ll x;
             cin >> x;
             s.insert(x);
        }
        //s.unique();
        //cout<<"Test "<< s.size()<<endl;
        if(s.size()>k)
        {
            cout<<"-1"<<endl;
            continue;
        }
        else
        {
            cout<<n*k<<endl;

            for(ll i=0 ; i<n; i++)
            {
                for(auto x: s)cout<<x<<" ";
                for(ll i =0 ;i<k-s.size();i++)
                {
                    cout<<"1 ";
                }
            }
            cout<<endl;
        }
    }
}