func_code_string: #include <bits/stdc++.h>   using namespace std;   bool cmp(pair<long long int, long long int> a,            pair<long long int, long long int> b) {     return a.first < b.first;   }   bool check(int a) {     int sum = 0;     while (a > 0) {       sum += (a % 10);       a /= 10;     }     if (sum == 10) return true;     return false;   }   bool prime[10005];   void seivertexe() {     memset(prime, 1, sizeof(prime));     prime[0] = 0;     prime[1] = 0;     for (long long int i = 2; i <= 10000; i++) {       if (prime[i] == 1) {         for (long long int j = i * i; j <= 10000; j += i) prime[j] = 0;       }     }   }   template <typename T>   std::string NumberToString(T Number) {     std::ostringstream ss;     ss << Number;     return ss.str();   }   bool isPrime(long long int n) {     if (n <= 1) return false;     if (n <= 3) return true;     if (n % 2 == 0 || n % 3 == 0) return false;     for (long long int i = 5; i * i <= n; i = i + 6)       if (n % i == 0 || n % (i + 2) == 0) return false;     return true;   }   long long int power(long long int x, long long int y) {     if (y == 0)       return 1;     else if (y % 2 == 0)       return (power(x, y / 2) % 1000000007 * power(x, y / 2) % 1000000007) %              1000000007;     else       return (x % 1000000007 *               (power(x, y / 2) % 1000000007 * power(x, y / 2) % 1000000007) %               1000000007) %              1000000007;   }   long long int factorial1(long long int n) {     return (n == 1 || n == 0)                ? 1                : (n % 1000000007 * factorial1(n - 1) % 1000000007) % 1000000007;   }   long long int fact(long long int n);   long long int nCr(long long int n, long long int r) {     return fact(n) % 1000000007 /            ((fact(r) % 1000000007 * fact(n - r) % 1000000007)) % 1000000007;   }   long long int fact(long long int n) {     long long int res = 1;     for (int i = 2; i <= n; i++) res = (res * i) % 1000000007;     return res % 1000000007;   }   void solve() {}   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     ;     long long int t;     cin >> t;     while (t--) {       long long int n;       cin >> n;       long long int arr[n + 1];       map<long long int, long long int> mp1, mp2, mp3;       for (long long int i = 1; i <= n; i++) {         cin >> arr[i];         mp1[arr[i]]++;       }       long long int k = 0;       long long int flag = 0;       long long int arr1[2 * n + 2];       for (long long int i = 1; i <= n; i++) {         long long int x = arr[i];         if (x > 2 * n) {           flag = 1;           cout << -1 <<   n ;           break;         }         if (mp2[x] > 0) {           flag = 1;           cout << -1 <<   n ;           break;         }         arr1[k++] = arr[i];         long long int y = arr[i] + 1;         while (mp1[y] != 0 || mp2[y] != 0) {           y++;         }         if (y > 2 * n) {           flag = 1;           cout << -1 <<   n ;           break;         } else {           mp2[y]++;           mp2[x]++;           arr1[k++] = y;         }       }       if (!flag) {         for (long long int i = 0; i < 2 * n; i++) {           cout << arr1[i] <<    ;         }         cout <<   n ;       }     }     return 0;   }   