ProblemB. Phoenix and Beauty

// Problem: B. Phoenix and Beauty
// Contest: Codeforces - Codeforces Round #638 (Div. 2)
// URL: https://codeforces.com/problemset/problem/1348/B
// Memory Limit: 256 MB
// Time Limit: 2000 ms
// 2022-03-01 16:52:57
// 
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
using namespace std;

#define rep(i,l,r) for(int i=(l);i<=(r);i++)
#define per(i,l,r) for(int i=(l);i>=(r);i--)
#define ll long long
#define pii pair<int, int>
#define mset(s,t) memset(s,t,sizeof(t))
#define mcpy(s,t) memcpy(s,t,sizeof(t))
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define SZ(x) ((int)(x).size())
#define mp make_pair

const ll mod = 1e9 + 7;

inline ll qmi (ll a, ll b) {
	ll ans = 1;
	while (b) {
		if (b & 1) ans = ans * a%mod;
		a = a * a %mod;
		b >>= 1;
	}
	return ans;
}
inline int read () {
	int x = 0, f = 0;
	char ch = getchar();
	while (!isdigit(ch)) f |= (ch=='-'),ch= getchar();
	while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
	return f?-x:x;
}
template<typename T> void print(T x) {
	if (x < 0) putchar('-'), x = -x;
	if (x >= 10) print(x/10);
	putchar(x % 10 + '0');
}
inline ll sub (ll a, ll b) {
	return ((a - b ) %mod + mod) %mod;
}
inline ll add (ll a, ll b) {
	return (a + b) %mod;
}
inline ll inv (ll a) {
	return qmi(a, mod - 2);
}
int a[1000];
vector<int> ans;
int n;
void solve() {
	int n, k;
	cin >> n >> k;
	set<int> s;
	for (int i = 0; i < n; i ++) {
		int t;
		cin >> t;
		s.insert(t);
	}
	if (s.size() > k) {
		puts("-1");
	}
	else {
		cout << n * k << endl;
		for (int i = 0; i < n; i ++) {
			for (auto t:s) cout << t << " ";
			for (int j = 0; j < k - s.size(); j ++)
				cout << 1 << " \n"[i == k - s.size()];
		}
		puts("");
	}
	
}
int main () {
    int t;
    t =1;
    cin >> t;
    while (t --) solve();
    return 0;
}

If the different number is greater than k No solution . Because it cannot occur periodically . We can construct such a sequence for k = 4 a b c d a b c d a b c d. In this way, we can meet the requirements of the topic . Describe the form of the answer to the question I was trying to find someone , But this and is hard to find . I don't know how to meet the requirements of the topic as much as possible . In fact, you can choose all the numbers greedily ( use set save , Because we can insert any number (1<= <=n), So the order between them doesn't matter );