#include <bits/stdc++.h>
#define int long long
#define debug puts("###");
using namespace std;

const int N=3e5+10;
int a[N],b[N],B[N]; 
inline void solve() {
	int n,m;//puts("1");
	scanf("%lld%lld",&n,&m);
	for (int i=1;i<=n;i++) scanf("%lld",&a[i]);
	for (int i=n-m+1;i<=n;i++) scanf("%lld",&b[i]);
	sort(a+1,a+n+1);
	sort(b+n-m+1,b+n+1);
	for (int i=n-m+1;i<=n;i++) if (a[i]>b[i]) {puts("-1");return ;}
	int suma=0,sumb=0;
	for (int i=n-m+1;i<=n;i++) suma+=a[i],sumb+=b[i];
	int step=sumb-suma,minb=b[n-m+1];
	if (step>n-m) {puts("-1");return ;} 
	priority_queue<int,vector<int>,greater<int> > q,q2;
	for (int i=1;i<=n-m;i++) q.push(a[i]);
	vector<int> v;
	for (int i=n-m+1;i<=n;i++) if (a[i]!=b[i]) v.push_back(i);
	int len=v.size();
	for (int i=n-m+1,j=0;j<len;i++,j++) b[i]=b[v[j]],q2.push(a[v[j]]);
	vector<int> ans;
	for (int i=n-m,cnt=n-m+1;i>=1;i--) {
		int x=q.top(),y=-1; q.pop();
		if (!q2.empty()) y=q2.top();
		if (x>=minb) {puts("-1");return ;}
		if (x==y) {
			q2.pop(); --step; ans.push_back(y);
			if (y+1==b[cnt]) ++cnt;
			else q2.push(y+1);
		}
		else {
			q.push(x+1); ans.push_back(x); q.pop();
		}
		if (i-1==step) {
			while (!q2.empty()) {
				int y=q2.top(); q2.pop();
				ans.push_back(y); if(y+1==b[cnt]) ++cnt;
				else q2.push(y+1);
			}
			break;
		}
	}
	
	len=ans.size();
	printf("%lld\n",len);
	for (int i=0;i<len;i++) printf("%lld ",ans[i]);if (len!=0) puts("");
}

signed main(void) {
	int t; cin>>t;
	while (t--) solve();
}