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.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.HashSet;
  import java.util.StringTokenizer;
  import java.util.ArrayList;
  import java.util.Collections;
  public class yibianguo{
      public static void main(String[]args) {
          FastScanner c = new FastScanner();
          int a = c.nextInt();
          for(int aa=0;aa<a;aa++){
              int b = c.nextInt();
              HashSet<Integer> h  = new HashSet<Integer>();
              int []z =new int[b]; 
              int []x=new int[b+1];
              int g =0;
              boolean i = true;
              ArrayList<Integer> d = new ArrayList<Integer>();
              for(int q= 0;q<b;q++){
                  z[q]= c.nextInt();
                  if(z[q]<=b&&h.add(z[q])){
                      x[z[q]]++;
                      h.add(z[q]);
                  }
                  else{
                      d.add((z[q]-1)/2);
                      g++;
                  }
              }
              int p =0;
              Collections.sort(d);
              for(int q= 1;q<b+1;q++){
                  if(x[q]==0){
                      if(d.get(p++)>=q){}
                      else{
                          i = false;
                          break;
                      }
                  }
              }
              if(i){
                  System.out.println(g);
              }
              else{
                  System.out.println(-1);
              }
          }
      System.out.close();
  }
  static class FastScanner {
      BufferedReader br;
      StringTokenizer st;
  
      public FastScanner() {
          try	{
              br = new BufferedReader(new InputStreamReader(System.in));
              st = new StringTokenizer(br.readLine());
          } catch (Exception e){e.printStackTrace();}
      }
  
      public String next() {
          if (st.hasMoreTokens())	return st.nextToken();
          try {st = new StringTokenizer(br.readLine());}
          catch (Exception e) {e.printStackTrace();}
          return st.nextToken();
      }
  
      public int nextInt() {return Integer.parseInt(next());}
  
      public long nextLong() {return Long.parseLong(next());}
  
      public double nextDouble() {return Double.parseDouble(next());}
  
      public String nextLine() {
          String line = "";
          if(st.hasMoreTokens()) line = st.nextToken();
          else try {return br.readLine();}catch(IOException e){e.printStackTrace();}
          while(st.hasMoreTokens()) line += " "+st.nextToken();
          return line;
      }
  }
  }
  