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: //Utilities
  import java.io.*;
  import java.util.*;
  
  public class C {
  	static int t;
  	static int n;
  	static long[] a;
  	static long[] fac;
  	
  	static final int MOD = 998244353;
  	
  	public static void main(String[] args) throws IOException {
  		fac = new long[200005];
  		fac[0] = 1;
  		for (int i = 1; i < 200005; i++) {
  			fac[i] = fac[i-1] * i % MOD;
  		}
  		t = in.iscan();
  		while (t-- > 0) {
  			run();
  		}
  		out.close();
  	} 
  	
  	static void run() throws IOException {
  		n = in.iscan(); a = new long[n];
  		for (int i = 0; i < n; i++) {
  			a[i] = in.lscan();
  		}
  		UTILITIES.sort(a, true);
  		long cntMax = 0, cntNextMax = 0;
  		long max = a[n-1], nextMax = 0;
  		for (int i = n-1; i >= 0; i--) {
  			if (a[i] == a[n-1]) {
  				cntMax++;
  			}
  			else {
  				nextMax = a[i];
  				break;
  			}
  		}
  		for (int i = n-1; i >= 0; i--) {
  			if (a[i] == nextMax) {
  				cntNextMax++;
  			}
  		}
  		if (cntMax == 1) {
  			if (max - nextMax > 1) {
  				out.println(0);
  				return;
  			}
  			long res = 0;
  			for (int i = n-1; i >= 1; i--) {
  				res = (res + cntNextMax * choose(i, (int)(cntNextMax)) % MOD * fac[(int)(cntNextMax)] % MOD * fac[(int)(n-cntNextMax-1)]) % MOD;
  			}
  			out.println(res);
  		}
  		else { // cntMax > 1
  			out.println(fac[n]);
  		}
  	}
  	
  	static long choose(int n, int k) {
  		if (k > n) {
  			return 0;
  		}
  		long a = fac[n];
  		long b = fac[k] * fac[n-k] % MOD;
  		return a * UTILITIES.fast_pow_mod(b, MOD-2, MOD) % MOD;
  	}
  	
  	static INPUT in = new INPUT(System.in);
  	static PrintWriter out = new PrintWriter(System.out);
  	private static class INPUT {
  
  		private InputStream stream;
  		private byte[] buf = new byte[1024];
  		private int curChar, numChars;
  
  		public INPUT (InputStream stream) {
  			this.stream = stream;
  		}
  
  		public INPUT (String file) throws IOException {
  			this.stream = new FileInputStream (file);
  		}
  
  		public int cscan () throws IOException {
  			if (curChar >= numChars) {
  				curChar = 0;
  				numChars = stream.read (buf);
  			}
  			
  			if (numChars == -1)
  				return numChars;
  
  			return buf[curChar++];
  		}
  
  		public int iscan () throws IOException {
  			int c = cscan (), sgn = 1;
  			
  			while (space (c))
  				c = cscan ();
  
  			if (c == '-') {
  				sgn = -1;
  				c = cscan ();
  			}
  
  			int res = 0;
  
  			do {
  				res = (res << 1) + (res << 3);
  				res += c - '0';
  				c = cscan ();
  			}
  			while (!space (c));
  
  			return res * sgn;
  		}
  
  		public String sscan () throws IOException {
  			int c = cscan ();
  			
  			while (space (c))
  				c = cscan ();
  
  			StringBuilder res = new StringBuilder ();
  
  			do {
  				res.appendCodePoint (c);
  				c = cscan ();
  			}
  			while (!space (c));
  
  			return res.toString ();
  		}
  
  		public double dscan () throws IOException {
  			int c = cscan (), sgn = 1;
  			
  			while (space (c))
  				c = cscan ();
  
  			if (c == '-') {
  				sgn = -1;
  				c = cscan ();
  			}
  
  			double res = 0;
  
  			while (!space (c) && c != '.') {
  				if (c == 'e' || c == 'E')
  					return res * UTILITIES.fast_pow (10, iscan ());
  				
  				res *= 10;
  				res += c - '0';
  				c = cscan ();
  			}
  
  			if (c == '.') {
  				c = cscan ();
  				double m = 1;
  
  				while (!space (c)) {
  					if (c == 'e' || c == 'E')
  						return res * UTILITIES.fast_pow (10, iscan ());
  
  					m /= 10;
  					res += (c - '0') * m;
  					c = cscan ();
  				}
  			}
  
  			return res * sgn;
  		}
  
  		public long lscan () throws IOException {
  			int c = cscan (), sgn = 1;
  			
  			while (space (c))
  				c = cscan ();
  
  			if (c == '-') {
  				sgn = -1;
  				c = cscan ();
  			}
  
  			long res = 0;
  
  			do {
  				res = (res << 1) + (res << 3);
  				res += c - '0';
  				c = cscan ();
  			}
  			while (!space (c));
  
  			return res * sgn;
  		}
  
  		public boolean space (int c) {
  			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
  		}
  	}
  
  	public static class UTILITIES {
  
  		static final double EPS = 10e-6;
  		
  		public static void sort(int[] a, boolean increasing) {
  			ArrayList<Integer> arr = new ArrayList<Integer>();
  			int n = a.length;
  			for (int i = 0; i < n; i++) {
  				arr.add(a[i]);
  			}
  			Collections.sort(arr);
  			for (int i = 0; i < n; i++) {
  				if (increasing) {
  					a[i] = arr.get(i);
  				}
  				else {
  					a[i] = arr.get(n-1-i);
  				}
  			}
  		}
  		
  		public static void sort(long[] a, boolean increasing) {
  			ArrayList<Long> arr = new ArrayList<Long>();
  			int n = a.length;
  			for (int i = 0; i < n; i++) {
  				arr.add(a[i]);
  			}
  			Collections.sort(arr);
  			for (int i = 0; i < n; i++) {
  				if (increasing) {
  					a[i] = arr.get(i);
  				}
  				else {
  					a[i] = arr.get(n-1-i);
  				}
  			}
  		}
  		
  		public static void sort(double[] a, boolean increasing) {
  			ArrayList<Double> arr = new ArrayList<Double>();
  			int n = a.length;
  			for (int i = 0; i < n; i++) {
  				arr.add(a[i]);
  			}
  			Collections.sort(arr);
  			for (int i = 0; i < n; i++) {
  				if (increasing) {
  					a[i] = arr.get(i);
  				}
  				else {
  					a[i] = arr.get(n-1-i);
  				}
  			}
  		}
  
  		public static int lower_bound (int[] arr, int x) {
  			int low = 0, high = arr.length, mid = -1;
  
  			while (low < high) {
  				mid = (low + high) / 2;
  
  				if (arr[mid] >= x)
  					high = mid;
  				else
  					low = mid + 1;
  			}
  
  			return low;
  		}
  
  		public static int upper_bound (int[] arr, int x) {
  			int low = 0, high = arr.length, mid = -1;
  
  			while (low < high) {
  				mid = (low + high) / 2;
  
  				if (arr[mid] > x)
  					high = mid;
  				else
  					low = mid + 1;
  			}
  
  			return low;
  		}
  		
  		public static void updateMap(HashMap<Integer, Integer> map, int key, int v) {
  			if (!map.containsKey(key)) {
  				map.put(key, v);
  			}
  			else {
  				map.put(key, map.get(key) + v);
  			}
  			if (map.get(key) == 0) {
  				map.remove(key);
  			}
  		}
  
  		public static long gcd (long a, long b) {
  			return b == 0 ? a : gcd (b, a % b);
  		}
  
  		public static long lcm (long a, long b) {
  			return a * b / gcd (a, b);
  		}
  
  		public static long fast_pow_mod (long b, long x, int mod) {
  			if (x == 0) return 1;
  			if (x == 1) return b;
  			if (x % 2 == 0) return fast_pow_mod (b * b % mod, x / 2, mod) % mod;
  
  			return b * fast_pow_mod (b * b % mod, x / 2, mod) % mod;
  		}
  
  		public static int fast_pow (int b, int x) {
  			if (x == 0) return 1;
  			if (x == 1) return b;
  			if (x % 2 == 0) return fast_pow (b * b, x / 2);
  
  			return b * fast_pow (b * b, x / 2);
  		}
  
  		public static long choose (long n, long k) {
  			k = Math.min (k, n - k);
  			long val = 1;
  
  			for (int i = 0; i < k; ++i)
  				val = val * (n - i) / (i + 1);
  
  			return val;
  		}
  
  		public static long permute (int n, int k) {
  			if (n < k) return 0;
  			long val = 1;
  
  			for (int i = 0; i < k; ++i)
  				val = (val * (n - i));
  
  			return val;
  		}
  		
  		// start of permutation and lower/upper bound template
  		public static void nextPermutation(int[] nums) {
  		    //find first decreasing digit
  		    int mark = -1;
  		    for (int i = nums.length - 1; i > 0; i--) {
  		        if (nums[i] > nums[i - 1]) {
  		            mark = i - 1;
  		            break;
  		        }
  		    }
  		 
  		    if (mark == -1) {
  		        reverse(nums, 0, nums.length - 1);
  		        return;
  		    }
  		 
  		    int idx = nums.length-1;
  		    for (int i = nums.length-1; i >= mark+1; i--) {
  		        if (nums[i] > nums[mark]) {
  		            idx = i;
  		            break;
  		        }
  		    }
  		 
  		    swap(nums, mark, idx);
  		 
  		    reverse(nums, mark + 1, nums.length - 1);
  		}
  		 
  		public static void swap(int[] nums, int i, int j) {
  		    int t = nums[i];
  		    nums[i] = nums[j];
  		    nums[j] = t;
  		}
  		 
  		public static void reverse(int[] nums, int i, int j) {
  		    while (i < j) {
  		        swap(nums, i, j);
  		        i++;
  		        j--;
  		    }
  		}
  		
  		static int lower_bound (int[] arr, int hi, int cmp) {
  			int low = 0, high = hi, mid = -1;
  			while (low < high) {
  				mid = (low + high) / 2;
  				if (arr[mid] >= cmp) high = mid;
  				else low = mid + 1;
  			}
  			return low;
  		}
  	 
  		static int upper_bound (int[] arr, int hi, int cmp) {
  			int low = 0, high = hi, mid = -1;
  			while (low < high) {
  				mid = (low + high) / 2;
  				if (arr[mid] > cmp) high = mid;
  				else low = mid + 1;
  			}
  			return low;
  		}
  		// end of permutation and lower/upper bound template
  	}
  }
  