1uVAUk - Online C++0x Compiler & Debugging Tool

#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b) {
    int x = 1;
    a %= M;
    while (b) {
        if (b & 1) x = (x * a) % M;
        a = (a * a) % M;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************


vector<int> a;

vector<int> consistency(int n){
	if(n&1) return {};

    vector<int> ans;
    sort(begin(a), end(a), greater<int>());

    unordered_map<int,int> mp;

    for(int i=0; i<n; i++){
        int val = a[i];
        if( mp.count(2*val)){
            mp[2*val]--;
            if(mp[2*val] == 0) mp.erase(2*val);
            ans.push_back(val);
        }
        else mp[val]++;
    }

    if(ans.size() == n/2) return ans;

    return {};
}


vector<int> practice(int n){


    return {};
}


void solve() {

    int n;
    cin>> n;

    a.resize(n);
    for(int i=0; i<n; i++) cin >> a[i];

    auto ans = consistency(n);
    if(ans.empty()) cout << "-1" << endl;
    for(auto& it : ans) cout << it << " "; cout << endl;


}


int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}