#include<bits/stdc++.h>
using namespace std;
int T,n;
int o[600005];
int fa[320000],dep[320000];
int pd[320000];
int zan[320000],ztop=0;
void in(int x,int y){
	if(x==y)return ;
	in(fa[x],y);
	zan[++ztop]=x;
}
int LCA(int x,int y){
	if(dep[x]<dep[y])swap(x,y);
	while(dep[x]>dep[y])x=fa[x];
	while(x!=y){
		x=fa[x];y=fa[y];
	}
	return x;
}
void sol(int x,int y){
	int lca=LCA(x,y);
	while(y!=lca){
		zan[++ztop]=y;
		y=fa[y];
	}
	zan[++ztop]=lca;
	in(x,lca);
}
int main(){
	//freopen("ans.out","w",stdout);
	cin>>T;
	while(T--){
		scanf("%d",&n);
		ztop=0;
		for(int i=1;i<=n;i++)pd[i]=0;
		for(int i=1;i<2*n;i++){
			scanf("%d",&o[i]);
			pd[o[i]]++;
		}
		o[1]=1;
		o[2*n-1]=1;
		pd[1]=2;
		int now1=0,reg=1;
		for(int i=1;i<2*n;i++){
			if(!o[i])break;
			if(now1&&fa[now1]==o[i]){
				now1=o[i];
			}
			else{
				fa[o[i]]=now1;
				dep[o[i]]=dep[now1]+1;
				now1=o[i];
			}
			reg=i;
		}
		int now2=0;
		for(int i=2*n-1;i;i--){
			if(!o[i])break;
			if(now2&&fa[now2]==o[i]){
				now2=o[i];
			}
			else{
				fa[o[i]]=now2;
				dep[o[i]]=dep[now2]+1;
				now2=o[i];
			}
		}
		int zz=1;while(pd[zz])zz++;
		sol(now1,now2);
		while(ztop){
			if(ztop==1){
				for(int i=zz;i<=n;i++){
					if(pd[i])continue;
					o[++reg]=i;
					o[++reg]=zan[ztop];
				}
				break;
			}
			if(zan[ztop-1]>zz){
				zan[++ztop]=zz;
				o[++reg]=zz;
				zz++;
				while(pd[zz])zz++;
			}
			else{
				o[++reg]=zan[ztop-1];
				ztop--;
			}
		}
		for(int i=1;i<2*n;i++){
			printf("%d ",o[i]);
		}puts("");
	}
}