description: Let's call a sequence of integers x_1, x_2, ..., x_k MEX-correct if for all i (1 ≤ i ≤ k) |x_i - \operatorname{MEX}(x_1, x_2, ..., x_i)| ≤ 1 holds. Where \operatorname{MEX}(x_1, ..., x_k) is the minimum non-negative integer that doesn't belong to the set x_1, ..., x_k. For example, \operatorname{MEX}(1, 0, 1, 3) = 2 and \operatorname{MEX}(2, 1, 5) = 0.
  
  You are given an array a consisting of n non-negative integers. Calculate the number of non-empty MEX-correct subsequences of a given array. The number of subsequences can be very large, so print it modulo 998244353. 
  
  Note: a subsequence of an array a is a sequence [a_{i_1}, a_{i_2}, ..., a_{i_m}] meeting the constraints 1 ≤ i_1 < i_2 < ... < i_m ≤ n. If two different ways to choose the sequence of indices [i_1, i_2, ..., i_m] yield the same subsequence, the resulting subsequence should be counted twice (i. e. two subsequences are different if their sequences of indices [i_1, i_2, ..., i_m] are not the same).
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 10^5) — the number of test cases.
  
  The first line of each test case contains a single integer n (1 ≤ n ≤ 5 ⋅ 10^5).
  
  The second line contains n integers a_1, a_2, ..., a_n (0 ≤ a_i ≤ n).
  
  The sum of n over all test cases doesn't exceed 5 ⋅ 10^5.
  
  Output
  
  For each test case, print a single integer — the number of non-empty MEX-correct subsequences of a given array, taken modulo 998244353.
  
  Example
  
  Input
  
  
  4
  3
  0 2 1
  2
  1 0
  5
  0 0 0 0 0
  4
  0 1 2 3
  
  
  Output
  
  
  4
  2
  31
  7
  
  Note
  
  In the first example, the valid subsequences are [0], [1], [0,1] and [0,2].
  
  In the second example, the valid subsequences are [0] and [1].
  
  In the third example, any non-empty subsequence is valid. 
solution: import static java.lang.Math.*;
  import java.util.*;
  import java.io.*;
  
  public class Solution {
      public static long find(int n, int[] a) {
          long mod = 998244353L;
          long res = 0;
          long[] dp1 = new long[n + 2];
          long[] dp2 = new long[n + 2];
          dp1[0] = 1;
          int min = Integer.MAX_VALUE;
          for (int i: a) min = min(min, i);
          if (min > 1) return 0;
          for (int x: a) {
  
              dp1[x+1] = (dp1[x+1] + dp1[x+1])%mod;
              dp1[x+1] = (dp1[x] + dp1[x + 1]) % mod;
              if (x-1 >= 0) {
                  dp2[x-1] = (dp2[x-1] + dp2[x-1])%mod;
              }
              if (x-1 >= 0) {
                  dp2[x-1] = (dp2[x-1] + dp1[x-1])%mod;
              }
              dp2[x+1] = (dp2[x+1]+dp2[x+1])%mod;
          }
          for (long l: dp1) {
              res = (res + l)%mod;
          }
          for (long l: dp2) {
              res = (res + l)%mod;
          }
  //        System.out.println("dp1: " + Arrays.toString(dp1));
  //        System.out.println("dp2: " + Arrays.toString(dp2));
          return (res-1 + mod) % mod;
      }
  
      public static void main(String[] args) throws Exception {
          InputReader fs = new InputReader(System.in);
          PrintWriter pw = new PrintWriter(System.out);
          int t = fs.readInt();
          for (int tt = 0; tt < t; tt++) {
              int n = fs.readInt();
              int[] a = fs.readIntArray(n);
              pw.println(find(n, a));
          }
          pw.flush();
          pw.close();
      }
  
      static class InputReader
      {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private 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 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
              {
                  res.appendCodePoint(c);
                  c = read();
              } while (!isSpaceChar(c));
              return res.toString();
          }
  
          public double readDouble() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-')
              {
                  sgn = -1;
                  c = read();
              }
              double res = 0;
              while (!isSpaceChar(c) && c != '.')
              {
                  if (c == 'e' || c == 'E')
                      return res * Math.pow(10, readInt());
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              if (c == '.')
              {
                  c = read();
                  double m = 1;
                  while (!isSpaceChar(c))
                  {
                      if (c == 'e' || c == 'E')
                          return res * Math.pow(10, readInt());
                      if (c < '0' || c > '9')
                          throw new InputMismatchException();
                      m /= 10;
                      res += (c - '0') * m;
                      c = read();
                  }
              }
              return res * sgn;
          }
  
          public long readLong() {
              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;
          }
  
          public boolean isSpaceChar(int c) {
              if (filter != null)
                  return filter.isSpaceChar(c);
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
          public int[] readIntArray(int n) {
              int[] a = new int[n];
              for (int i = 0; i < n; i++) {
                  a[i] = readInt();
              }
              return a;
          }
          public int[] readIntArrayShifted(int n) {
              int[] a = new int[n + 1];
              for (int i = 0; i < n; i++) {
                  a[i + 1] = readInt();
              }
              return a;
          }
          public long[] readLongArray(int n) {
              long[] a = new long[n];
              for (int i = 0; i < n; i++) {
                  a[i] = readLong();
              }
              return a;
          }
          public String next() {
              return readString();
          }
  
          interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
          }
      }
  
  }