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 sys, math
  #sys.setrecursionlimit(10**6)
  INF = float('inf')
  #mod = 10**9 + 7
  mod = 998244353
  input = lambda: sys.stdin.readline().rstrip()
  li = lambda: list(map(int, input().split()))
  
  t = int(input())
  
  for _ in range(t):
      N = int(input())
      A = li()
      x = N+5
      data = [0] * x
      data2 = [0] * x
      ans = 0
      for i in range(N):
          a = data[A[i]]
          b = data2[A[i]]
          c = data2[A[i]+2]
          if A[i] >= 1:
              a += data[A[i]-1]
          if A[i] >= 2:
              b += data[A[i]-2]
          if A[i] == 0:
              a += 1
          if A[i] == 1:
              b += 1
          a %= mod; b %= mod
          ans += a + b + c
          ans %= mod
  
          data[A[i]] += a
          data[A[i]] %= mod
          data2[A[i]] += b
          data2[A[i]+2] += c
          data2[A[i]] %= mod
  
      print(ans % mod)
  
  
  