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.util.*;
  
  public class P1569C {
  	static int mod = 998244353;
  
  	public static void main(String[] args) {
  		Scanner s = new Scanner(System.in);
  		int t = s.nextInt();
  		while (t-- > 0) {
  			long n = s.nextInt(), max = Long.MIN_VALUE, a = 0, b = 0;
  			int[] arr = new int[(int) n];
  			long ans = 1, sans = 1;
  			for (int i = 0; i < n; i++) {
  				arr[i] = s.nextInt();
  				if (arr[i] > max) {
  					max = arr[i];
  				}
  			}
  			for (int i = 0; i < n; i++) {
  				if (arr[i] == max)
  					a++;
  				if (arr[i] == max - 1)
  					b++;
  			}
  			//PIE
  			for (int i = 2; i <= n; i++) {
  				if (i != b + 1)
  					sans = (sans * i)%mod;
  				ans = (ans*i)%mod;
  			}
  			if (a > 1) {
  				System.out.println(ans);
  			} else {
  				if (b > 0) {
  					System.out.println((ans - sans + mod) % mod);
  				} else {
  					System.out.println(0);
  				}
  			}
  		}
  		s.close();
  	}
  
  	public static long factorial(int n) {
  		int ans = 1;
  		for (int i = 1; i <= n; i++)
  			ans = (ans * i) % mod;
  		return ans;
  	}
  }
  