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.*;
  
  import java.io.*;
  
  public class cf {
      static Reader sc = new Reader();
      static PrintWriter out = new PrintWriter(System.out);
      static long mod = (long) 1e9 + 7;
  
      public static void main(String[] args) {
          int tc = sc.ni();
          long mod= 998244353;
          long[] fact=new long[200001];
          fact[0]=1;
          for(int i=1;i<=200000;i++){
              fact[i]=((long)fact[i-1]*i)%mod;
          }
          
          while (tc-- > 0) {
              int n=sc.ni();
              int[] arr=sc.nai(n);
              sort(arr);
              if(arr[n-1]-arr[n-2]>1){
                  out.println(0);
              }else if(arr[n-1]==arr[n-2]){
                  out.println(fact[n]);
              }else{
                  int freq=0;
                  int idx=n-2;
                  while(idx>=0 && arr[idx]==arr[n-2]){
                      freq++;
                      idx--;
                  }
                  long res=fact[n],curr=0;
                  for(int i=0;i<n;i++){
                      long calc=ncr(i,freq,fact,mod);
                      curr=(curr+calc)%mod;
                  }
                  curr = (curr * fact[freq]) % mod;
                  curr = (curr * fact[n - freq-1]) % mod;
                  res=(res-curr+mod)%mod;
                  out.println(res);
              }
          }
          out.close();
  
      }
  
      static long ncr(int i,int j,long[] fact,long mod){
          if(i<j) return 0;
          if(i==j) return 1;
          long res=(fact[i-j]*fact[j])%mod;
          return (fact[i]*modInverse(res,mod))%mod;
      }
  
      static long modInverse(long a, long m) {
          if (m == 1)
              return -1;
          if (gcd(a, m) != 1)
              return -1;
          long[] g = gcdExtended(a, m);
          long ans = (g[0] + m) % m;
          return ans;
      }
  
      // result contains {x,y,gcd}
      static long[] gcdExtended(long a, long b) {
          if (b == 0) {
              return new long[] { 1, 0, a };
          }
          long[] sa = gcdExtended(b, a % b);
          // x0=y1,y0=x1-y1*(a/b);
          long x0 = sa[1];
          long y0 = sa[0] - (sa[1] * (a / b));
          return new long[] { x0, y0, sa[2] };
      }
      
  
      public static long pow(long a, long b, long m) {
          if (b == 0) {
              return 1;
          }
          if (b % 2 == 0) {
              return pow((a * a) % m, b / 2, m) % m;
          } else {
              return (a * pow((a * a) % m, b / 2, m)) % m;
          }
      }
  
      // snippets
  
      static class Pair implements Comparable<Pair> {
          int x;
          int y;
  
          Pair(int x, int y) {
              this.x = x;
              this.y = y;
  
          }
  
          @Override
          public int compareTo(Pair o) {
              if (this.x > o.x)
                  return 1;
              else if (this.x < o.x)
                  return -1;
              else {
                  if (this.y > o.y)
                      return 1;
                  else if (this.y < o.y)
                      return -1;
                  else
                      return 0;
              }
          }
  
          public int hashCode() {
              int ans = 1;
              ans = x * 31 + y * 13;
              return ans;
          }
  
          @Override
          public boolean equals(Object o) {
              if (this == o) {
                  return true;
              }
              if (o == null) {
                  return false;
              }
              if (this.getClass() != o.getClass()) {
                  return false;
              }
              Pair other = (Pair) o;
              if (this.x == other.x && this.y == other.y) {
                  return true;
              }
              return false;
          }
  
      }
  
      static void add_map(HashMap<Integer, Integer> map, int v) {
          if (!map.containsKey(v)) {
              map.put(v, 1);
          } else {
              map.put(v, map.get(v) + 1);
          }
      }
  
      static void remove_map(HashMap<Integer, Integer> map, int v) {
          if (map.containsKey(v)) {
              map.put(v, map.get(v) - 1);
              if (map.get(v) == 0)
                  map.remove(v);
          }
      }
  
      static int gcd(int a, int b) {
          if (b == 0)
              return a;
          return gcd(b, a % b);
      }
  
      static long gcd(long a, long b) {
          if (b == 0)
              return a;
          return gcd(b, a % b);
      }
  
      static void sort(int[] arr) {
          // shuffle
          Random rand = new Random();
          for (int i = 0; i < arr.length; i++) {
              int j = rand.nextInt(i + 1);
              int tmp = arr[i];
              arr[i] = arr[j];
              arr[j] = tmp;
          }
          Arrays.sort(arr);
      }
  
      static void sort(long[] arr) {
          // shuffle
          Random rand = new Random();
          for (int i = 0; i < arr.length; i++) {
              int j = rand.nextInt(i + 1);
              long tmp = arr[i];
              arr[i] = arr[j];
              arr[j] = tmp;
          }
          Arrays.sort(arr);
      }
  
      static boolean isPrime(int n) {
          if (n <= 1)
              return false;
          if (n <= 3)
              return true;
          if (n % 2 == 0 || n % 3 == 0)
              return false;
          double sq = Math.sqrt(n);
  
          for (int i = 5; i <= sq; i = i + 6)
              if (n % i == 0 || n % (i + 2) == 0)
                  return false;
          return true;
      }
  
      static boolean isPrime(long n) {
          if (n <= 1)
              return false;
          if (n <= 3)
              return true;
          if (n % 2 == 0 || n % 3 == 0)
              return false;
          double sq = Math.sqrt(n);
  
          for (int i = 5; i <= sq; i = i + 6)
              if (n % i == 0 || n % (i + 2) == 0)
                  return false;
          return true;
      }
  
      static void print_arr(int A[]) {
          for (int i : A) {
              System.out.print(i + " ");
          }
          System.out.println();
      }
  
      static void print_arr(long A[]) {
          for (long i : A) {
              System.out.print(i + " ");
          }
          System.out.println();
      }
  
      static void print_arr(char A[]) {
          for (char i : A) {
              System.out.print(i + " ");
          }
          System.out.println();
      }
  
      static int min(int a, int b) {
          return Math.min(a, b);
      }
  
      static int min(int a, int b, int c) {
          return Math.min(a, Math.min(b, c));
      }
  
      static int min(int a, int b, int c, int d) {
          return Math.min(a, Math.min(b, Math.min(c, d)));
      }
  
      static int max(int a, int b) {
          return Math.max(a, b);
      }
  
      static int max(int a, int b, int c) {
          return Math.max(a, Math.max(b, c));
      }
  
      static int max(int a, int b, int c, int d) {
          return Math.max(a, Math.max(b, Math.max(c, d)));
      }
  
      static long min(long a, long b) {
          return Math.min(a, b);
      }
  
      static long min(long a, long b, long c) {
          return Math.min(a, Math.min(b, c));
      }
  
      static long min(long a, long b, long c, long d) {
          return Math.min(a, Math.min(b, Math.min(c, d)));
      }
  
      static long max(long a, long b) {
          return Math.max(a, b);
      }
  
      static long max(long a, long b, long c) {
          return Math.max(a, Math.max(b, c));
      }
  
      static long max(long a, long b, long c, long d) {
          return Math.max(a, Math.max(b, Math.max(c, d)));
      }
  
      static int max(int A[]) {
          int max = Integer.MIN_VALUE;
          for (int i = 0; i < A.length; i++) {
              max = Math.max(max, A[i]);
          }
          return max;
      }
  
      static int min(int A[]) {
          int min = Integer.MAX_VALUE;
          for (int i = 0; i < A.length; i++) {
              min = Math.min(min, A[i]);
          }
          return min;
      }
  
      static long max(long A[]) {
          long max = Long.MIN_VALUE;
          for (int i = 0; i < A.length; i++) {
              max = Math.max(max, A[i]);
          }
          return max;
      }
  
      static long min(long A[]) {
          long min = Long.MAX_VALUE;
          for (int i = 0; i < A.length; i++) {
              min = Math.min(min, A[i]);
          }
          return min;
      }
  
      static long sum(int A[]) {
          long sum = 0;
          for (int i : A) {
              sum += i;
          }
          return sum;
      }
  
      static long sum(long A[]) {
          long sum = 0;
          for (long i : A) {
              sum += i;
          }
          return sum;
      }
  
      static ArrayList<Integer> sieve(int n) {
          ArrayList<Integer> primes = new ArrayList<>();
          boolean[] isPrime = new boolean[n];
          Arrays.fill(isPrime, true);
          isPrime[0] = isPrime[1] = false;
          for (int i = 2; i * i <= n; i++) {
              if (isPrime[i]) {
                  for (int j = i * i; j < n; j += i) {
                      isPrime[j] = false;
                  }
              }
          }
          for (int i = 2; i < n; i++) {
              if (isPrime[i])
                  primes.add(i);
          }
          return primes;
      }
  
      static class Reader {
          BufferedReader br;
          StringTokenizer st;
  
          Reader() {
              br = new BufferedReader(new InputStreamReader(System.in));
              st = new StringTokenizer("");
          }
  
          Reader(File f) throws FileNotFoundException {
              br = new BufferedReader(new FileReader(f));
              st = new StringTokenizer("");
          }
  
          String next() {
              while (!st.hasMoreTokens())
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                  }
              return st.nextToken();
          }
  
          int ni() {
              return Integer.parseInt(next());
          }
  
          long nl() {
              return Long.parseLong(next());
          }
  
          double nextDouble() {
              return Double.parseDouble(next());
          }
  
          int[] nai(int n) {
              int[] a = new int[n];
              for (int i = 0; i < n; i++)
                  a[i] = ni();
              return a;
          }
  
          long[] nal(int n) {
              long[] a = new long[n];
              for (int i = 0; i < n; i++)
                  a[i] = nl();
              return a;
          }
      }
  
  }