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.*;
  import java.util.*;
  
  /**
   * A simple template for competitive programming problems.
   */
  public class Solution {
      //InputReader in = new InputReader("input.txt");
      final InputReader in = new InputReader(System.in);
  
      final PrintWriter out = new PrintWriter(System.out);
      final int mod = 998244353;
      void solve() {
          int t = in.nextInt();
          long[] fact = new long[2000034]; fact[0] = 1;
          for(int i=1; i<fact.length; i++) {
              fact[i] = (fact[i-1] * i)%mod;
          }
          while(t-->0) {
              int n = in.nextInt();
              int[] arr = in.nextArray(n);
              shuffle(arr);
              int max = 0;
              int maxCount = 0;
              for(int i=0; i<n; i++) {
                  if(arr[i]>max) {
                      maxCount = 1;
                      max = arr[i];
                  } else if(arr[i]==max) {
                      maxCount++;
                  }
              }
              if(maxCount>1 || n==1) {
                  out.println(fact[n]);
                  continue;
              }
              int sCount = 0;
              for(int i=0; i<n; i++) {
                  if(arr[i]==max-1) {
                      sCount++;
                  }
              }
              if(sCount==0) {
                  out.println(0);
                  continue;
              }
              long ans = (fact[n] - ((fact[n]*modInverse(sCount+1, mod))%mod))%mod;
              out.println(ans<0 ? ans+mod : ans);
          }
      }
      public static long modInverse(long a, long m) {
          long mod = m;
          long x = 0, y = 1, lastx = 1, lasty = 0, temp;
          while (m != 0) {
              long q = a / m;
              long r = a % m;
  
              a = m;
              m = r;
  
              temp = x;
              x = lastx - q*x;
              lastx = temp;
  
              temp = y;
              y = lasty - q*y;
              lasty = temp;
          }
          return (lastx % mod + mod) % mod;
      }
  
  	public class LST {
  
      /* *********************************** */
      /* CHANGE HERE FOR OTHER FUNCTIONALITY */
  
          private class Node {
              long ans;
              int fl;
              int ll;
              int length;
              int f;
              int l;
  
              void setLeaf(int i, int val) {
                  ans = 1;
                  fl = 1;
                  ll = 1;
                  f = val;
                  l = val;
                  length = 1;
              }
  
              void merge(LST.Node a, LST.Node b) {
                  f = a.f;
                  l = b.l;
                  ans = a.ans + b.ans;
                  if (a.l <= b.f) {
                      ans += (long) a.ll * b.fl;
                  }
                  fl = a.fl;
                  ll = b.ll;
                  if (a.fl == a.length && a.l <= b.f) {
                      fl += b.fl;
                  }
                  if (b.ll == b.length && a.l <= b.f) {
                      ll += a.ll;
                  }
                  length = a.length + b.length;
              }
  
              void split(LST.Node left, LST.Node right) {
              }
  
              void updateSingle(int val) {
                  ans = 1;
                  fl = 1;
                  ll = 1;
                  f = val;
                  l = val;
                  length = 1;
              }
          }
      /* CHANGE HERE FOR OTHER FUNCTIONALITY */
      /* *********************************** */
  
      private final int n;
      private final Node[] tree;
      private int ql, qr, val;
  
      public LST(int[] arr) {
          n = arr.length;
          int h = 32 - Integer.numberOfLeadingZeros(n-1) + 1;
          tree = new Node[1<<h];
          build(1, 0, arr.length-1, arr);
      }
  
      private void build(int i, int l, int r, int[] arr) {
          if (l == r) {
              tree[i] = new Node();
              tree[i].setLeaf(l, arr[l]);
          } else {
              int m = (l+r+1) / 2;
              build(2*i, l, m-1, arr);
              build(2*i+1, m, r, arr);
              tree[i] = new Node();
              tree[i].merge(tree[2*i], tree[2*i+1]);
          }
      }
  
      public void update(int ql, int qr, int val) {
          this.ql = ql;
          this.qr = qr;
          this.val = val;
          updateHelper(1, 0, n-1);
      }
  
      private void updateHelper(int i, int l, int r) {
          if (qr < l || ql > r) return;
          if (qr >= r && ql <= l) tree[i].updateSingle(val);
          else {
              tree[i].split(tree[2*i], tree[2*i+1]);
              int m = (l+r+1) / 2;
              updateHelper(2*i, l, m-1);
              updateHelper(2*i+1, m, r);
              tree[i].merge(tree[2*i], tree[2*i+1]);
          }
      }
  
      public Node query(int ql, int qr) {
          this.ql = ql;
          this.qr = qr;
          return queryHelper(1, 0, n-1);
      }
  
      private Node queryHelper(int i, int l, int r) {
          if (qr < l || ql > r) return null;
          if (qr >= r && ql <= l) return tree[i];
          tree[i].split(tree[2*i], tree[2*i+1]);
          int m = (l+r+1) / 2;
  
          Node ansLeft = queryHelper(2*i, l, m-1);
          Node ansRight = queryHelper(2*i + 1, m, r);
          if (ansLeft == null) return ansRight;
          if (ansRight == null) return ansLeft;
          Node answer = new Node();
          answer.merge(ansLeft, ansRight);
          return answer;
      }
  }
  
      private void shuffle(int[] a) {
          int n = a.length;
          Random random = new Random();
          random.nextInt();
          for (int i = 0; i < n; i++) {
              int change = i + random.nextInt(n - i);
              swap(a, i, change);
          }
      }
  
      private static void swap(int[] a, int i, int j) {
          int helper = a[i];
          a[i] = a[j];
          a[j] = helper;
      }
  
      public static void main(final String[] args) throws FileNotFoundException {
          final Solution s = new Solution();
          final Long t1 = System.currentTimeMillis();
          s.solve();
          System.err.println(System.currentTimeMillis() - t1 + " ms");
          s.out.close();
      }
  
      public Solution() throws FileNotFoundException {
      }
  
      private static class InputReader {
          private final InputStream stream;
          private final byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          Random r = new Random();
  
          InputReader(final InputStream stream) {
              this.stream = stream;
          }
  
          InputReader(final String fileName) {
              InputStream stream = null;
              try {
                  stream = new FileInputStream(fileName);
              } catch (final FileNotFoundException e) {
                  e.printStackTrace();
              }
              this.stream = stream;
          }
  
          int[] nextArray(final int n) {
              final int[] arr = new int[n];
              for (int i = 0; i < n; i++)
                  arr[i] = nextInt();
              return arr;
          }
  
          int[][] nextMatrix(final int n, final int m) {
              final int[][] matrix = new int[n][m];
              for (int i = 0; i < n; i++)
                  for (int j = 0; j < m; j++)
                      matrix[i][j] = nextInt();
              return matrix;
          }
  
          String nextLine() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              final StringBuilder res = new StringBuilder();
              do {
                  res.appendCodePoint(c);
                  c = read();
              } while (!isEndOfLine(c));
              return res.toString();
          }
  
          String nextString() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              final StringBuilder res = new StringBuilder();
              do {
                  res.appendCodePoint(c);
                  c = read();
              } while (!isSpaceChar(c));
              return res.toString();
          }
  
          long nextLong() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              long res = 0;
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
  
          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;
          }
  
          double nextDouble() {
              return Double.parseDouble(nextString());
          }
  
          private int read() {
              if (numChars == -1)
                  throw new InputMismatchException();
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (final IOException e) {
                      throw new InputMismatchException();
                  }
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
  
          private boolean isSpaceChar(final int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          private boolean isEndOfLine(final int c) {
              return c == '\n' || c == '\r' || c == -1;
          }
      }
  
  }