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.*;
  
  public class new1{
  	
  	
  	public static void main(String[] args)  throws IOException{
      	BufferedWriter output = new BufferedWriter(new OutputStreamWriter(System.out));
  		FastReader s = new FastReader();
  		int t = s.nextInt();
      	for(int z = 0; z < t; z++) {
      		int n = s.nextInt();
      		TreeSet<Integer> ts=  new TreeSet<Integer>();
      		HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
      		int[] arr  = new int[n + 1];
      		for(int i = 0; i < n; i++) {
      			int val = s.nextInt();
      			if(val <= n && arr[val] == 0) arr[val] = 1;
      			else {
  	    			if(ts.contains(val)) {
  	    				map.put(val, map.get(val) + 1);
  	    			}
  	    			else {
  	    				ts.add(val);
  	    				map.put(val, 1);
  	    			}
      			}
      		}
      		boolean pos= true;
      		int count = 0;
      		for(int i = 1; i <= n; i++) {
      			if(arr[i] == 1) continue;
      			else {
      				if(ts.last() <= 2 * i) {
      					pos = false; break;
      				}
      				int v1 = ts.higher(2 * i);
      				int fr = map.get(v1) - 1;
      				if(fr == 0) {
      					ts.remove(v1);
      					map.remove(v1);
      				}
      				else map.put(v1, fr);
      				count++;
      			}
      		}
      		if(!ts.isEmpty()) pos= false;
      		if(!pos) System.out.println(-1);
      		else System.out.println(count);
      		
      		
      		
      		
      	}
      	//output.flush();
  
      }
  }
  
  
  class FastReader {
      BufferedReader br;
      StringTokenizer st;
      public FastReader() {
          br = new BufferedReader(new InputStreamReader(System.in));
      }
      String next() {
          while (st == null || !st.hasMoreElements()) {
              try {
                  st = new StringTokenizer(br.readLine());
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          return st.nextToken();
      }
   
      public int nextInt() {
          return Integer.parseInt(next());
      }
   
      long nextLong() {
          return Long.parseLong(next());
      }
   
      double nextDouble() {
          return Double.parseDouble(next());
      }
   
      String nextLine() {
          String str = "";
          try {
              str = br.readLine();
          } catch (IOException e) {
              e.printStackTrace();
          }
          return str;
  }}