#include<bits/stdc++.h>

using namespace std;

#define int long long
#define pb push_back
#define F first 
#define S second 

const int mol=998244353;
const int N = 3e5+5;

vector<int>node[N];
int a[N*2], lst[N];
bool vis[N], vv[N];
vector<int>un;
int iu=0;
void dfs(int v, int pre){
    vv[v]=1;
    iu++;
    if(a[iu+1]==pre) return;
    while(a[iu+1]){ dfs(a[iu+1], v), iu++;if(!a[iu]) a[iu]=v;if(a[iu+1]==pre) return;}
    if(v==pre){

        while(un.size()>=2&&un[un.size()-2]<v){
            a[++iu]=un.back(), un.pop_back(), a[++iu]=un.back(), un.pop_back(), a[++iu]=a[iu-2];a[++iu]=v;
        }
        while(un.size()) a[++iu]=un.back(), a[++iu]=v, un.pop_back();
        vector<pair<int, int>>ha;
        for(int i: node[v]){
            if(!vv[i]) ha.pb({lst[i], i});
        }
        sort(ha.begin(), ha.end());
        for(auto t: ha){
            dfs(t.S, v);
        }
        return;
    }
        while(un.size()&&un.back()<pre){
            a[iu++]=un.back();un.pop_back();
            if(un.size()&&un.back()<v) 
                a[iu++]=un.back(), un.pop_back(),
                a[iu++]=a[iu-2], a[iu++]=v;
            else a[iu++]=v;
        }
        if(lst[v]>iu){
            while(un.size()>=2&&un[un.size()-2]<v){
                a[++iu]=un.back(), un.pop_back(), a[++iu]=un.back(), un.pop_back(), a[++iu]=a[iu-2];a[++iu]=v;
            }
            while(un.size()) a[++iu]=un.back(), a[++iu]=v, un.pop_back();
            vector<pair<int, int>>ha;
            for(int i: node[v]){
                if(!vv[i]) ha.pb({lst[i], i});
            }
            sort(ha.begin(), ha.end());
            for(auto t: ha){
                dfs(t.S, v);
            }
        }
        else return;
    
}

void solve(){
    int n;
    cin>>n;

    for(int i=1;i<=n;i++) vis[i]=0, node[i].clear(), vv[i]=0;
    un.clear();
    a[n*2]=0;
    for(int i=1;i<=n*2-1;i++){
        cin>>a[i];
        lst[a[i]]=i;
        if(i>1&&a[i-1]&&a[i]){
            node[a[i-1]].pb(a[i]);
            node[a[i]].pb(a[i-1]);
            vis[a[i]]=1;
        }
    }
    for(int i=1;i<=n;i++){
        if(!vis[i]) un.pb(i);
    }
    reverse(un.begin(), un.end());
    int r;
    if(!a[1]&&!a[n]){
        for(int i=2;i<=n;i++) cout<<"1 "<<i<<" ";
        cout<<"1\n";
        return;
    }
    else r=max(a[1], a[n]); 
    dfs(r, r);
    for(int i=1;i<=n*2-1;i++) cout<<a[i]<<" ";cout<<"\n";
}

signed main(){
    ios::sync_with_stdio(0);cin.tie(0);
    int t;
    cin>>t;
    while(t--)
    solve();
    return 0;
}