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.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.io.PrintWriter;
  import java.util.Arrays;
  import java.io.BufferedWriter;
  import java.util.InputMismatchException;
  import java.io.IOException;
  import java.io.Writer;
  import java.io.OutputStreamWriter;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          OutputWriter out = new OutputWriter(outputStream);
          CJuryMeeting solver = new CJuryMeeting();
          int testCount = Integer.parseInt(in.next());
          for (int i = 1; i <= testCount; i++)
              solver.solve(i, in, out);
          out.close();
      }
  
      static class CJuryMeeting {
          public void solve(int testNumber, InputReader in, OutputWriter out) {
              int n = in.nextInt();
              Integer[] a = new Integer[n];
              for (int i = 0; i < n; i++) {
                  a[i] = in.nextInt();
              }
              Arrays.sort(a);
              int mod = 998244353;
              int max = a[n - 1];
              int lmax = a[n - 2];
              if (max >= lmax + 2) {
                  out.println(0);
                  return;
              }
              if (max == lmax) {
                  long res = 1;
                  for (int i = 1; i <= n; i++) {
                      res = res * i % mod;
                  }
                  out.println(res);
                  return;
              }
              int t = n - 2;
              int cnt = 0;
              while (t >= 0 && a[t] == lmax) {
                  cnt++;
                  t--;
              }
  
              long all = 1;
              for (int i = 1; i <= n; i++) {
                  all = all * i % mod;
              }
              long t1 = 1;
              for (int i = 1; i <= cnt; i++) {
                  t1 = t1 * i % mod;
              }
              int last = cnt + 1;
              long t2 = 1;
              for (int i = last + 1; i <= n; i++) {
                  t2 = t2 * i % mod;
              }
              out.println((all - t2 * t1 % mod + mod) % mod);
          }
  
      }
  
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private InputReader.SpaceCharFilter filter;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          public int read() {
              if (numChars == -1) {
                  throw new InputMismatchException();
              }
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
                  if (numChars <= 0) {
                      return -1;
                  }
              }
              return buf[curChar++];
          }
  
          public int nextInt() {
              int c = read();
              while (isSpaceChar(c)) {
                  c = read();
              }
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              int res = 0;
              do {
                  if (c < '0' || c > '9') {
                      throw new InputMismatchException();
                  }
                  res *= 10;
                  res += c - '0';
                  c = read();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
  
          public String nextString() {
              int c = read();
              while (isSpaceChar(c)) {
                  c = read();
              }
              StringBuilder res = new StringBuilder();
              do {
                  if (Character.isValidCodePoint(c)) {
                      res.appendCodePoint(c);
                  }
                  c = read();
              } while (!isSpaceChar(c));
              return res.toString();
          }
  
          public boolean isSpaceChar(int c) {
              if (filter != null) {
                  return filter.isSpaceChar(c);
              }
              return isWhitespace(c);
          }
  
          public static boolean isWhitespace(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          public String next() {
              return nextString();
          }
  
          public interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
  
          }
  
      }
  
      static class OutputWriter {
          private final PrintWriter writer;
  
          public OutputWriter(OutputStream outputStream) {
              writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
          }
  
          public OutputWriter(Writer writer) {
              this.writer = new PrintWriter(writer);
          }
  
          public void close() {
              writer.close();
          }
  
          public void println(long i) {
              writer.println(i);
          }
  
          public void println(int i) {
              writer.println(i);
          }
  
      }
  }
  
  