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: from math import factorial
  
  MOD = 998244353
  
  
  def fact(n, skip):
      f = 1
      sub = 1
      for i in range(2, n + 1):
          f = (f * i) % MOD
          if i != skip:
              sub = (sub * i) % MOD
  
      return f, sub
  
  
  def smart_fact(n):
      r = 1
  
      while n > 1:
          if (n / MOD) % 2 == 1:
              r = MOD - r
          r = r * factorial(n % MOD) % MOD
          n //= MOD
  
      return r
  
  
  def main():
      t = int(input())
  
      for _ in range(t):
          n = int(input())
  
          words = input().split(" ")
  
          jury = (int(i) for i in words)
          jury = sorted(jury, reverse=True)
  
          first, second = jury[:2]
  
          diff = first - second
          # print(diff)
  
          if diff == 0:
              res, _ = fact(n, 0)
              print(res)
              continue
  
          if diff == 1:
              times = 1
              for t in jury[2:]:
                  if second == t:
                      times += 1
  
              res, sub = fact(n, times + 1)
              res = (res - sub + MOD) % MOD
              print(res)
              continue
  
          print(0)
  
  
  if __name__ == "__main__":
      main()
  