description: Paprika loves permutations. She has an array a_1, a_2, ..., a_n. She wants to make the array a permutation of integers 1 to n.
  
  In order to achieve this goal, she can perform operations on the array. In each operation she can choose two integers i (1 ≤ i ≤ n) and x (x > 0), then perform a_i := a_i mod x (that is, replace a_i by the remainder of a_i divided by x). In different operations, the chosen i and x can be different.
  
  Determine the minimum number of operations needed to make the array a permutation of integers 1 to n. If it is impossible, output -1.
  
  A permutation is an array consisting of n distinct integers from 1 to n in arbitrary order. For example, [2,3,1,5,4] is a permutation, but [1,2,2] is not a permutation (2 appears twice in the array) and [1,3,4] is also not a permutation (n=3 but there is 4 in the array).
  
  Input
  
  Each test contains multiple test cases. The first line contains a single integer t (1 ≤ t ≤ 10^4) — the number of test cases. Description of the test cases follows.
  
  The first line of each test case contains an integer n (1 ≤ n ≤ 10^5).
  
  The second line of each test case contains n integers a_1, a_2, ..., a_n. (1 ≤ a_i ≤ 10^9).
  
  It is guaranteed that the sum of n over all test cases does not exceed 2 ⋅ 10^5.
  
  Output
  
  For each test case, output the minimum number of operations needed to make the array a permutation of integers 1 to n, or -1 if it is impossible.
  
  Example
  
  Input
  
  
  4
  2
  1 7
  3
  1 5 4
  4
  12345678 87654321 20211218 23571113
  9
  1 2 3 4 18 19 5 6 7
  
  
  Output
  
  
  1
  -1
  4
  2
  
  Note
  
  For the first test, the only possible sequence of operations which minimizes the number of operations is: 
  
    * Choose i=2, x=5. Perform a_2 := a_2 mod 5 = 2. 
  
  
  
  For the second test, it is impossible to obtain a permutation of integers from 1 to n.
solution: import java.io.*;
  import java.util.Arrays;
  import java.util.Random;
  import java.util.StringTokenizer;
  import java.util.TreeMap;
  
  public class codeforces_761_C {
      private static void solve(FastIOAdapter in, PrintWriter out) {
          int n = in.nextInt();
          int[] a = in.readArray(n);
  
          ruffleSort(a);
          int res = 0;
          boolean[] g = new boolean[n + 1];
          int cur = 1;
          for (int i = 0; i < n; i++) {
              if (i > 0 && a[i - 1] == a[i] || a[i] > n) {
                  while (g[cur]) {
                      cur++;
                  }
                  if (cur < (a[i] + 1) / 2) {
                      g[cur] = true;
                      res++;
                  } else {
                      res = -1;
                      break;
                  }
              } else {
                  g[a[i]] = true;
              }
          }
          out.println(res);
      }
  
      public static void main(String[] args) throws Exception {
          try (FastIOAdapter ioAdapter = new FastIOAdapter()) {
              int count = 1;
              count = ioAdapter.nextInt();
              while (count-- > 0) {
                  solve(ioAdapter, ioAdapter.out);
              }
          }
      }
  
      static void ruffleSort(int[] arr) {
          int n = arr.length;
          Random rnd = new Random();
          for (int i = 0; i < n; ++i) {
              int tmp = arr[i];
              int randomPos = i + rnd.nextInt(n - i);
              arr[i] = arr[randomPos];
              arr[randomPos] = tmp;
          }
          Arrays.sort(arr);
      }
  
      static class FastIOAdapter implements AutoCloseable {
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
          public PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter((System.out))));
          StringTokenizer st = new StringTokenizer("");
  
          String next() {
              while (!st.hasMoreTokens())
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              return st.nextToken();
          }
  
          String nextLine() {
              try {
                  return br.readLine();
              } catch (IOException e) {
                  e.printStackTrace();
                  return null;
              }
          }
  
          int nextInt() {
              return Integer.parseInt(next());
          }
  
          int[] readArray(int n) {
              int[] a = new int[n];
              for (int i = 0; i < n; i++) a[i] = nextInt();
              return a;
          }
  
          long[] readArrayLong(int n) {
              long[] a = new long[n];
              for (int i = 0; i < n; i++) a[i] = nextLong();
              return a;
          }
  
          long nextLong() {
              return Long.parseLong(next());
          }
  
          @Override
          public void close() throws Exception {
              out.flush();
              out.close();
              br.close();
          }
      }
  }
  