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 Main {
  
  	private static final int MOD = 998244353;
  	
  	public static void main(String[] args) {
  		FastScanner fs=new FastScanner();
  
  		/******  CODE STARTS HERE  *****/
  		//------------------------------------------------------------------------------------------------------------
  		
  		int t = fs.nextInt();
  		while(t-->0) {
  			int n = fs.nextInt();
  			int[] a = fs.readArray(n);
  			int[] dp1 = new int[n+2];
  			int[] dp2 = new int[n+2];
  			
  			for(int i=0; i<n; i++) {
  				
  				int x = a[i];
  				
  				dp1[x+1] = (dp1[x+1] + dp1[x+1]) % MOD;
  				dp1[x+1] = (dp1[x+1] + dp1[x]) % MOD;
  				
  				dp2[x+1] = (dp2[x+1] + dp2[x+1]) % MOD;
  				if(x!=0)dp2[x-1] = (dp2[x-1] + dp2[x-1]) % MOD;
  				
  				if(x!=0)dp2[x-1] = (dp2[x-1] + dp1[x-1]) % MOD;
  	
  				if(x==0) 
  					dp1[1] += 1;
  				else if(x==1) 
  					dp2[0] += 1;
  			}
  			
  //			for(int i=0; i<n; i++) {
  //				for(int j=0; j<=n+1; j++) {
  //					System.out.print(dp1[i][j]+" ");
  //				}
  //				System.out.println();
  //			}
  //			
  //			System.out.println();
  //			
  //			for(int i=0; i<n; i++) {
  //				for(int j=0; j<=n+1; j++) {
  //					System.out.print(dp2[i][j]+" ");
  //				}
  //				System.out.println();
  //			}
  			
  			int ans = 0;
  			for(int i=0; i<n+2; i++)
  				ans = (ans + (dp1[i] + dp2[i]) % MOD) % MOD;
  			
  			System.out.println(ans);
  		}
  	}
      
  	//******  CODE ENDS HERE  *****
  	//----------------------------------------------------------------------------------------------------------------
  	
  	static void sort(int[] a) {
  		ArrayList<Integer> l=new ArrayList<>();
  		for (int i:a) l.add(i);
  		Collections.sort(l);
  		for (int i=0; i<a.length; i++) a[i]=l.get(i);
  	}
  	
  	
  	//----------- FastScanner class for faster input---------------------------
  	static class FastScanner {
  		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  		StringTokenizer st=new StringTokenizer("");
  		String next() {
  			while (!st.hasMoreTokens())
  				try {
  					st=new StringTokenizer(br.readLine());
  				} catch (IOException e) {
  					e.printStackTrace();
  				}
  			return st.nextToken();
  		}
  		
  		int nextInt() {
  			return Integer.parseInt(next());
  		}
  		int[] readArray(int n) {
  			int[] a=new int[n];
  			for (int i=0; i<n; i++) a[i]=nextInt();
  			return a;
  		}
  		long nextLong() {
  			return Long.parseLong(next());
  		}
  	}
  }