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 sys import stdin
  # input=stdin.buffer.readline
  input=lambda : stdin.readline().strip()
  lin=lambda :list(map(int,input().split()))
  iin=lambda :int(input())
  main=lambda :map(int,input().split())
  from math import ceil,sqrt,factorial,log
  from collections import deque
  from bisect import bisect_left
  mod=998244353
  # mod=1000000007
  def moduloinverse(a):
  	return(pow(a,mod-2,mod))
  def solve(we):
  	n=iin()
  	l=lin()
  	l.sort()
  	if l[-1]-l[-2]>=2:
  		print(0)
  		return
  	fac=[1]
  	for i in range(1,n+1):
  		fac.append((fac[-1]*i)%mod)
  	if l[-1]==l[-2] or l[-1]==l[0]:
  		print((fac[-1])%mod)
  	else:
  		t=l.count(l[-2])
  		q=n-t-1
  		ans=fac[n-1]
  		for i in range(1,n-t):
  			z=(fac[n-1-i]*fac[q])%mod
  			z=(z*moduloinverse(fac[q-i]))%mod
  			ans=(ans+z)%mod
  		print((fac[n]-ans)%mod)
  
  
  
  
  
  qwe=1
  qwe=iin()
  for _ in range(qwe):
  	solve(_+1)