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 collections
  # import random
  # import math
  # import itertools
  # import math
  # mport math
  # from collections import defaultdict
  # import itertools
  # from sys import stdin, stdout
  # import math
  # import math
  import sys
  
  # import bisect
  # import operator
  # from decimal import Decimal
  
  # sys.setrecursionlimit(10**6)
  
  p2D = lambda x: print(*x, sep="\n")
  
  
  def II(): return int(sys.stdin.buffer.readline())
  
  
  def MI(): return map(int, sys.stdin.buffer.readline().split())
  
  
  def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
  
  
  def LLI(rows_number): return [LI() for _ in range(rows_number)]
  
  
  def BI(): return sys.stdin.buffer.readline().rstrip()
  
  
  def SI(): return sys.stdin.buffer.readline().rstrip().decode()
  
  
  def li(): return [int(i) for i in input().split()]
  
  
  def lli(rows): return [li() for _ in range(rows)]
  
  
  def si(): return input()
  
  
  def ii(): return int(input())
  
  
  def ins(): return input().split()
  
  facts = [1]*200010
  mod = 998244353
  
  for i in range(2,200010):
      facts[i] = (facts[i-1]*i)%mod
  
  #print(facts[:20])
  def solve():
      n = II()
      a = LI()
      b = sorted(a)
      #print(b)
      cb = b.count(b[-1])
      if cb>1:
          return facts[n]
      else:
          p = b.count(b[-2])
          if b[-1]-b[-2]>1:
              return 0
          if n == 2:
              return 1
          #print(facts[n])
          res = 1
          for i in range(p+2,n+1):
              res= (res*i)%mod
          return (facts[n]- (res*facts[p])+mod)%mod
  
  def main():
      #print('finish '+ str(solve()), flush=True)
      for _ in range(II()):
          sys.stdout.write(str(solve()) + "\n")
  
      #     z += str(ans) + '\n'
      # print(len(ans), ' '.join(map(str, ans)), sep='\n')
      # stdout.write(z)
  
  
  # for interactive problems
  # print("? {} {}".format(l,m), flush=True)
  # or print this after each print statement
  # sys.stdout.flush()
  
  
  if __name__ == "__main__":
      main()