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.util.*;
  import java.util.Map.Entry;
  
  import java.math.*;
  import java.io.*;
  
  public class Main {
  	public static void main(String[] args) throws FileNotFoundException {
  		InputReader in = new InputReader(System.in);
  		// Scanner in = new Scanner(System.in);
  		// Scanner in = new Scanner(new BufferedReader(new
  		// InputStreamReader(System.in)));
  		PrintWriter out = new PrintWriter(System.out);
  		// InputReader in = new InputReader(new
  		// File("ethan_traverses_a_tree.txt"));
  		// PrintWriter out = new PrintWriter(new
  		// File("ethan_traverses_a_tree-output.txt"));
  
  		long mod = 998244353;
  
  		int pi = in.nextInt();
  		for (int qi = 0; qi < pi; qi++) {
  			int n = in.nextInt();
  			int[] a = new int[n];
  			for (int i = 0; i < n; i++) {
  				a[i] = in.nextInt();
  			}
  
  			long[][] dp = new long[n + 10][2];
  			dp[0][0] = 1;
  			for (int i = 0; i < n; i++) {
  				int v = a[i];
  
  				Map<Integer, Long> map0 = new HashMap<Integer, Long>();
  				Map<Integer, Long> map1 = new HashMap<Integer, Long>();
  
  				if (v > 0) {
  					map1.put(v - 1, (dp[v - 1][0] + dp[v - 1][1] + dp[v - 1][1]) % mod);
  				}
  				map0.put(v + 1, (dp[v + 1][0] + dp[v + 1][0] + dp[v][0]) % mod);
  				map1.put(v + 1, (dp[v + 1][1] + dp[v + 1][1]) % mod);
  
  				for (Integer key : map0.keySet()) {
  					long value = map0.get(key);
  					dp[key][0] = value;
  				}
  
  				for (Integer key : map1.keySet()) {
  					long value = map1.get(key);
  					dp[key][1] = value;
  				}
  			}
  
  			long ans = 0;
  			for (int i = 0; i < dp.length; i++) {
  				ans = (ans + dp[i][0] + dp[i][1]) % mod;
  			}
  			ans = (ans + mod - 1) % mod;
  			out.printf("%d\n", ans);
  		}
  
  		out.close();
  	}
  
  	static class InputReader {
  		BufferedReader br;
  		StringTokenizer st;
  
  		public InputReader(File f) {
  			try {
  				br = new BufferedReader(new FileReader(f));
  			} catch (FileNotFoundException e) {
  				e.printStackTrace();
  			}
  		}
  
  		public InputReader(InputStream in) {
  			br = new BufferedReader(new InputStreamReader(in));
  		}
  
  		public String next() {
  			while (st == null || !st.hasMoreTokens()) {
  				try {
  					st = new StringTokenizer(br.readLine());
  				} catch (IOException e) {
  					e.printStackTrace();
  				}
  			}
  			return st.nextToken();
  		}
  
  		public boolean hasNext() {
  			while (st == null || !st.hasMoreTokens()) {
  				String s = null;
  				try {
  					s = br.readLine();
  				} catch (IOException e) {
  					e.printStackTrace();
  				}
  				if (s == null)
  					return false;
  				st = new StringTokenizer(s);
  			}
  			return true;
  		}
  
  		public int nextInt() {
  			return Integer.parseInt(next());
  		}
  
  		public long nextLong() {
  			return Long.parseLong(next());
  		}
  
  		public double nextDouble() {
  			return Double.parseDouble(next());
  		}
  	}
  }