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 java.io.*;
  import java.util.*;
  
  public class btry2 {
      //--------------------------INPUT READER---------------------------------//
      static class fs {
          public BufferedReader br;
          StringTokenizer st = new StringTokenizer("");
  
          public fs() { this(System.in); }
          public fs(InputStream is) {
              br = new BufferedReader(new InputStreamReader(is));
          }
          String next() {
              while (!st.hasMoreTokens()) {
                  try { st = new StringTokenizer(br.readLine()); }
                  catch (IOException e) { e.printStackTrace(); }
              }
              return st.nextToken();
          }
  
          int ni() { return Integer.parseInt(next()); }
          long nl() { return Long.parseLong(next()); }
          double nd() { return Double.parseDouble(next()); }
          String ns() { return next(); }
  
          int[] na(long nn) {
              int n = (int) nn;
              int[] a = new int[n];
              for (int i = 0; i < n; i++) a[i] = ni();
              return a;
          }
  
          long[] nal(long nn) {
              int n = (int) nn;
              long[] l = new long[n];
              for(int i = 0; i < n; i++) l[i] = nl();
              return l;
          }
      }
      //-----------------------------------------------------------------------//
  
      //---------------------------PRINTER-------------------------------------//
      static class Printer {
          static PrintWriter w;
          public Printer() {this(System.out);}
          public Printer(OutputStream os) {
              w = new PrintWriter(os);
          }
          public void p(int i) {w.println(i);}
          public void p(long l) {w.println(l);}
          public void p(double d) {w.println(d);}
          public void p(String s) { w.println(s);}
          public void pr(int i) {w.print(i);}
          public void pr(long l) {w.print(l);}
          public void pr(double d) {w.print(d);}
          public void pr(String s) { w.print(s);}
          public void pl() {w.println();}
          public void close() {w.close();}
      }
      //-----------------------------------------------------------------------//
  
      //--------------------------VARIABLES------------------------------------//
      static fs sc = new fs();
      static OutputStream outputStream = System.out;
      static Printer w = new Printer(outputStream);
      static long lma = Long.MAX_VALUE, lmi = Long.MIN_VALUE;
      static long ima = Integer.MAX_VALUE, imi = Integer.MIN_VALUE;
      static long mod = 998244353 ;
      //-----------------------------------------------------------------------//
  
      //--------------------------ADMIN_MODE-----------------------------------//
      private static void ADMIN_MODE() throws IOException {
          if (System.getProperty("ONLINE_JUDGE") == null) {
              w = new Printer(new FileOutputStream("output.txt"));
              sc = new fs(new FileInputStream("input.txt"));
          }
      }
      //-----------------------------------------------------------------------//
  
      //----------------------------START--------------------------------------//
      public static void main(String[] args)
              throws IOException {
  
          ADMIN_MODE();
  
          int t = sc.ni();while(t-->0)
              solve();
  
  
          w.close();
      }
  
      static void solve() throws IOException {
          int n = sc.ni();
          int[] arr = sc.na(n);
          // 3 cases ->
          // 0 1 2 3 4 5
          // 0 1 2 3 4 6
          // 0 1 2 3 5 3
          // mex[0] = []
          // mex2[0] = [1], [1 1]
          // mex[1] = [0]
          // mex2[1] = [0 2]
          // mex[2] = [0 1], [0 0 1 1]
          // mex1[2] = [0 1 3], [0 0 1 1 3 3]
          long[] mex = new long[n+5], mex2 = new long[n+5];
          long ans = 0;
          for(int i = 0; i < n; i++) {
              if(arr[i]==0) {
                  long total = 1;
                  total += mex[1]; // 0 0
                  total += mex2[1]; // 0 2 0
                  ans += total;
                  ans %= mod;
                  mex[1] += mex[1]+1; // 0 0
                  mex[1] %= mod;
                  mex2[1] += mex2[1]; // 0 2 0
                  mex2[1] %= mod;
              } else if(arr[i]==1) {
                  long total = 1;
                  total += mex[1]; // 0 1
                  total += mex[2];
                  total += mex2[0]; // 1 1
                  total += mex2[2]; // 0 1 3 1
                  ans += total;
                  ans %= mod;
                  mex2[0] += mex2[0]+1;
                  mex2[0] %= mod;
                  mex[2] += mex[1] + mex[2];
                  mex[2] %= mod;
                  mex2[2] += mex2[2];
                  mex2[2] %= mod;
              } else {
                  long total = 0;
                  total += mex[arr[i]]; // 1 2 3 4
                  total += mex[arr[i]+1]; // 1 2 3 4 4
                  total += mex[arr[i]-1]; // 1 2 4
                  total += mex2[arr[i]-1]; // 1 2 4 4
                  total += mex2[arr[i]+1]; // 1 2 3 4 6 4
                  ans += total;
                  ans %= mod;
                  mex[arr[i]+1] += mex[arr[i]]+mex[arr[i]+1];
                  mex[arr[i]+1] %= mod;
                  mex2[arr[i]-1] += mex[arr[i]-1] + mex2[arr[i]-1];
                  mex2[arr[i]-1] %= mod;
                  mex2[arr[i]+1] += mex2[arr[i]+1];
                  mex2[arr[i]+1] %= mod;
              }
          }
          w.p(ans);
      }
  }