description: n people gathered to hold a jury meeting of the upcoming competition, the i-th member of the jury came up with a_i tasks, which they want to share with each other.
  
  First, the jury decides on the order which they will follow while describing the tasks. Let that be a permutation p of numbers from 1 to n (an array of size n where each integer from 1 to n occurs exactly once).
  
  Then the discussion goes as follows:
  
    * If a jury member p_1 has some tasks left to tell, then they tell one task to others. Otherwise, they are skipped. 
    * If a jury member p_2 has some tasks left to tell, then they tell one task to others. Otherwise, they are skipped. 
    * ... 
    * If a jury member p_n has some tasks left to tell, then they tell one task to others. Otherwise, they are skipped. 
    * If there are still members with tasks left, then the process repeats from the start. Otherwise, the discussion ends. 
  
  
  
  A permutation p is nice if none of the jury members tell two or more of their own tasks in a row. 
  
  Count the number of nice permutations. The answer may be really large, so print it modulo 998 244 353.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 10^4) — the number of test cases.
  
  The first line of the test case contains a single integer n (2 ≤ n ≤ 2 ⋅ 10^5) — number of jury members.
  
  The second line contains n integers a_1, a_2, ..., a_n (1 ≤ a_i ≤ 10^9) — the number of problems that the i-th member of the jury came up with.
  
  The sum of n over all test cases does not exceed 2 ⋅ 10^5.
  
  Output
  
  For each test case, print one integer — the number of nice permutations, taken modulo 998 244 353.
  
  Example
  
  Input
  
  
  4
  2
  1 2
  3
  5 5 5
  4
  1 3 3 7
  6
  3 4 2 1 3 3
  
  
  Output
  
  
  1
  6
  0
  540
  
  Note
  
  Explanation of the first test case from the example:
  
  There are two possible permutations, p = [1, 2] and p = [2, 1]. For p = [1, 2], the process is the following:
  
    1. the first jury member tells a task; 
    2. the second jury member tells a task; 
    3. the first jury member doesn't have any tasks left to tell, so they are skipped; 
    4. the second jury member tells a task. 
  
  
  
  So, the second jury member has told two tasks in a row (in succession), so the permutation is not nice.
  
  For p = [2, 1], the process is the following:
  
    1. the second jury member tells a task; 
    2. the first jury member tells a task; 
    3. the second jury member tells a task. 
  
  
  
  So, this permutation is nice.
solution: 
  import java.io.*;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.Random;
  import java.util.StringTokenizer;
  
  public class Main {
      static InputReader sc = new InputReader(System.in);
      static PrintWriter out = new PrintWriter(System.out);
  
  
      static long inv(long a, long b) {
          return 1 < a ? b - inv(b % a, a) * b / a : 1;
      }
  
      static long mi(long a) {
          return inv(a, mod);
      }
  
      static long[] factorial = new long[200001];
      static long mod = 998244353;
  
      static void precomputeFactorial() {
          factorial[0] = 1;
          for (int i = 1; i < factorial.length; i++) {
              factorial[i] = (factorial[i - 1] * i) % mod;
          }
      }
  
      public static void main(String[] args) throws IOException {
  
          precomputeFactorial();
          int t = sc.nextInt();
  
          while (t-- > 0) {
              int n = sc.nextInt();
              long[] A = new long[n];
  
              HashMap<Long, Integer> map = new HashMap<>();
              for (int i = 0; i < n; i++) {
                  A[i] = sc.nextLong();
  
                  if(!map.containsKey(A[i])){
                      map.put(A[i], 0);
                  }
                  map.put(A[i], map.get(A[i]) + 1);
              }
              shuffle(A);
              Arrays.sort(A);
  
              long max = A[n - 1];
              long secondMax = A[n - 2];
  
              if (max - secondMax > 1) {
                  out.println(0);
              } else if (max - secondMax == 0) {
                  out.println(factorial[n]);
              } else {
                  int k = map.get(secondMax);
                  /*for(int i = n - 2; i >= 0; i--){
                      if(A[i] == secondMax){
                          k++;
                      }else {
                          break;
                      }
                  }
                   */
  
                  long ans = (factorial[n] + mod - (factorial[n] * mi(k + 1)) % mod) % mod;
                  out.println((int) ans);
              }
          }
  
          out.flush();
          out.close();
      }
  
  
      static class InputReader {
          BufferedReader reader;
          StringTokenizer tokenizer;
  
          public InputReader(InputStream stream) {
              reader = new BufferedReader(new InputStreamReader(stream), 32768);
              tokenizer = null;
          }
  
  
          String next() {
              while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                  try {
                      tokenizer = new StringTokenizer(reader.readLine());
                  } catch (IOException e) {
                      throw new RuntimeException(e);
                  }
              }
              return tokenizer.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 = reader.readLine();
              } catch (IOException e) {
                  throw new RuntimeException(e);
              }
              return str;
          }
      }
  
      public static void shuffle(int[] a) {
          Random get = new Random();
          for (int i = 0; i < a.length; i++) {
              int r = get.nextInt(a.length);
              int temp = a[i];
              a[i] = a[r];
              a[r] = temp;
          }
      }
  
      public static void shuffle(long[] a) {
          Random get = new Random();
          for (int i = 0; i < a.length; i++) {
              int r = get.nextInt(a.length);
              long temp = a[i];
              a[i] = a[r];
              a[r] = temp;
          }
      }
  
  
  }
  