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.util.Random;
  import java.io.Writer;
  import java.io.OutputStreamWriter;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author keyurjain
   */
  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);
          TaskC solver = new TaskC();
          int testCount = Integer.parseInt(in.next());
          for (int i = 1; i <= testCount; i++)
              solver.solve(i, in, out);
          out.close();
      }
  
      static class TaskC {
          static final int MOD = 998244353;
          static final int N = (int) (2e5 + 5);
          static final int[] factorial = new int[N];
          static final int[] ifactorial = new int[N];
  
          public void solve(int testNumber, InputReader in, OutputWriter out) {
              init();
              int n = in.readInt();
              int[] arr = in.readIntArray(n);
              Sorting.shuffleAndSort(arr);
  
              if (arr[n - 1] > arr[n - 2] + 1) {
                  out.printLine(0);
              } else if (arr[n - 1] == arr[n - 2]) {
                  out.printLine(factorial[n]);
              } else {
                  int totalPermutations = factorial[n];
                  int invalidPermutations = 0;
                  int countPenultimate = 0;
                  for (int i : arr) {
                      if (i == arr[n - 1] - 1) {
                          countPenultimate++;
                      }
                  }
                  for (int i = countPenultimate; i < n; i++) {
                      int right = n - i - 1;
                      int left = i;
                      if (left < countPenultimate) continue;
                      int elementsRemaining = n - 1 - countPenultimate;
                      int elementsNeeded = left - countPenultimate;
                      int leftPermutations = multiplySafe(nCr(elementsRemaining, elementsNeeded), factorial[left]);
                      int rightPermuations = factorial[right];
                      invalidPermutations = (int) ((1L * invalidPermutations + multiplySafe(leftPermutations, rightPermuations)) % MOD);
                  }
                  int validPermutations = (totalPermutations - invalidPermutations) % MOD;
                  if (validPermutations < 0) validPermutations += MOD;
                  out.printLine(validPermutations);
              }
          }
  
          private int nCr(int n, int r) {
              int numerator = factorial[n];
              int denominator = multiplySafe(ifactorial[n - r], ifactorial[r]);
              return multiplySafe(numerator, denominator);
          }
  
          private int modPow(int a, int b) {
              int ans = 1;
              while (b > 0) {
                  if ((b & 1) == 1) {
                      ans = multiplySafe(ans, a);
                  }
                  a = multiplySafe(a, a);
                  b >>= 1;
              }
              return ans;
          }
  
          private void init() {
              if (factorial[0] == 0) {
                  factorial[0] = 1;
                  ifactorial[0] = 1;
                  for (int i = 1; i < N; i++) {
                      factorial[i] = multiplySafe(factorial[i - 1], i);
                      ifactorial[i] = modPow(factorial[i], MOD - 2);
                  }
              }
          }
  
          private int multiplySafe(int a, int b) {
              return (int) ((1L * a * b) % 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[] readIntArray(int size) {
              int[] array = new int[size];
              for (int i = 0; i < size; i++) {
                  array[i] = readInt();
              }
              return array;
          }
  
          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 readInt() {
              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 readString() {
              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 readString();
          }
  
          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 printLine(int i) {
              writer.println(i);
          }
  
      }
  
      static class Sorting {
          public static void shuffleAndSort(int[] arr) {
              shuffleArray(arr);
              Arrays.sort(arr);
          }
  
          public static void shuffleArray(int[] arr) {
              int n = arr.length;
              Random rnd = new Random();
              for (int i = 0; i < n; ++i) {
                  int tmp = arr[i];
                  int randomPos = i + rnd.nextInt(n - i);
                  arr[i] = arr[randomPos];
                  arr[randomPos] = tmp;
              }
          }
  
      }
  }
  
  