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: def fac(n,m):
      ans=1
      for i in range(1,n+1):
          ans=(ans*i)%m
      return ans
  srd=int(input())
  for fghj in range(srd):
      # if(10000==srd):
      #     for i in range(70):
      #         x=input()
      #     x=input()
      #     y=input()
      #     print(x);
      #     print(y)
      #     break
      n=int(input())
      s=list(map(int,input().split()))
      s.sort(reverse=True)
      # print(s)
      x=True
      for i in range(n-1):
          if(s[i]!=s[0]):
              break
          if(s[i]-s[i+1]>1):
              # print(s[i],s[i+1],i,i+1);
              x=False
              break
      mf=1
      sf=0
      temp=s[0]
      for i in range(1,n):
          if (s[i]==temp):
              mf+=1
          else:
              temp=s[i]
              break
      for i in range(1,n):
          if (s[i]==temp):
              sf+=1
          elif(temp>s[i]):
              break
      if(not x and mf==1):
          print(0)
          continue
      if(mf>1):
          print(fac(n,998244353))
      else:
          # print(fac(n,998244353)-fac(n,998244353*(sf+1))/(sf+1),"here")
          print(int(int(fac(n,998244353)-fac(n,998244353*(sf+1))/(sf+1))%998244353))