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代码：

#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <queue>
#include <utility>
#include <map>
#include <set>
using namespace std;

// #define IS_ATCODER
// #define IS_MULTI_TESTS
// #define USE_CIN

#ifndef ONLINE_JUDGE
#include <atcoder/all>
using mint = atcoder::modint998244353;
#else
#ifdef IS_ATCODER
#include <atcoder/all>
using mint = atcoder::modint998244353;
#endif
#endif

#define mp make_pair
#define fi first
#define se second
#define bg begin()
#define ed end()
#define pb push_back
#define sz(a) int(a.size())
using ll = long long;
using pii = pair <int, int>;

inline int read(){
    int ret = 0;
    char ch = ' ', c = getchar();
    while(!('0' <= c && c <= '9')) ch = c, c = getchar();
    while('0' <= c && c <= '9'){
        ret = ret * 10 + (c ^ 48);
        c = getchar();
    }
    return ch == '-' ? -ret : ret;
}

map<int, int> cnt, empty_map;
vector<pii> vct[2];
vector<int> ans;
void calc(vector<pii> &vec){
    for(int i = 0; i < sz(vec); i += 2){
        auto [_00, _01] = vec[i];
        auto [_10, _11] = vec[i + 1];
        if(_00 > _01) swap(_00, _10), swap(_01, _11);
        while(_00){
            ans.pb(_01);
            ans.pb(_11);
            _00--;
            _10--;
        }
        while(_10){
            ans.pb(_11);
            _10--;
        }
    }
}
void solve(){
    int n = read();
    for(int i = 0; i < n; i++) cnt[read()]++;
    if(sz(cnt) & 1){
        printf("-1\n");
        return ;
    }
    for(auto [x, y]: cnt){
        vct[y & 1].pb(mp(y, x));
    }
    cnt.clear();
    cnt = empty_map;
    if((sz(vct[0]) & 1) || (sz(vct[1]) & 1)){
        printf("-1\n");
        return ;
    }
    sort(vct[0].bg, vct[0].ed);
    sort(vct[1].bg, vct[1].ed);
    calc(vct[0]), calc(vct[1]);
    vct[0].clear(), vct[0].shrink_to_fit();
    vct[1].clear(), vct[1].shrink_to_fit();
    for(int x: ans) printf("%d ", x);
    printf("\n");
    ans.clear(), ans.shrink_to_fit();
}

int main(){
#ifdef USE_CIN
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
#endif
#ifdef IS_MULTI_TESTS
    int T;
    #ifdef USE_CIN
        cin >> T;
    #else
        T = read();
    #endif
    while(T--) solve();
#else
    solve();
#endif
    return 0;
}