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 PaprikaandPermutation {
  
      public static void main(String args[]) throws IOException {
  
          FastReader sc = new FastReader();
          PrintWriter out = new PrintWriter(System.out);
  
          int tc, i, j;
          String s;
          char p;
  
          tc = sc.nextInt();
          while (tc-- > 0) {
              int n = sc.nextInt();
              int arr[] = sc.readArray(n);
              sc.sort(arr);
              TreeSet<Integer> set = new TreeSet<>();
              ArrayList<Integer> ls = new ArrayList<>();
  
              for(i = 1; i<=n; i++)
                  set.add(i);
  
              for(i = 0; i<n; i++) {
                  if(set.contains(arr[i]))
                      set.remove(arr[i]);
                  else
                      ls.add(arr[i]);
              }
  
              Collections.sort(ls);
              boolean flag = true;
              int ans = 0;
  
              for(int v : ls) {
                  i = set.pollFirst();
                  if(v==i) continue;
                  if(v-i<=0  || v%(v-i) != i) {
                      flag = false;
                      break;
                  }
                  ans++;
              }
              if(flag)
                  out.println(ans);
              else
                  out.println(-1);
          }
          out.close();
      }
  	
  
  
  /*--------------------------------------------------------
  ----------------------------------------------------------*/
  
  
      //Pair Class
  
      public static class Pair implements Comparable<Pair> {
          int x, y;
  
          Pair(int x, int y) {
              this.x = x;
              this.y = y;
          }
  
          @Override
          public int compareTo(Pair o) {
              return this.x - o.x;
          }
      }
  
      /*
  		FASTREADER
  	*/
      static 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();
          }
  
          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;
          }
  
          /*DEFINED BY ME*/
  
          //READING ARRAY
          int[] readArray(int n) {
              int arr[] = new int[n];
              for (int i = 0; i < n; i++)
                  arr[i] = nextInt();
              return arr;
          }
  
          //COLLECTIONS SORT
          void sort(int arr[]) {
              ArrayList<Integer> l = new ArrayList<>();
              for (int i : arr)
                  l.add(i);
              Collections.sort(l);
              for (int i = 0; i < arr.length; i++)
                  arr[i] = l.get(i);
          }
  
          //EUCLID'S GCD
          int gcd(int a, int b) {
              if (b != 0)
                  return gcd(b, a % b);
              else
                  return a;
          }
  
          void swap(int arr[], int i, int j) {
              int temp = arr[i];
              arr[i] = arr[j];
              arr[j] = temp;
          }
      }
  }