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: #include <bits/stdc++.h>
  using namespace std;
  template <typename... T>
  void show(T&&... args) {
    ((cerr << args << " "), ...);
  }
  template <typename F, typename S>
  ostream& operator<<(ostream& os, const pair<F, S>& p) {
    return os << "(" << p.first << ", " << p.second << ")";
  }
  template <typename T>
  ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    typename vector<T>::const_iterator it;
    for (it = v.begin(); it != v.end(); it++) {
      if (it != v.begin()) os << ", ";
      os << *it;
    }
    return os << "}";
  }
  template <typename T>
  ostream& operator<<(ostream& os, const set<T>& v) {
    os << "[";
    typename set<T>::const_iterator it;
    for (it = v.begin(); it != v.end(); it++) {
      if (it != v.begin()) os << ", ";
      os << *it;
    }
    return os << "]";
  }
  template <typename T>
  ostream& operator<<(ostream& os, const multiset<T>& v) {
    os << "[";
    typename multiset<T>::const_iterator it;
    for (it = v.begin(); it != v.end(); it++) {
      if (it != v.begin()) os << ", ";
      os << *it;
    }
    return os << "]";
  }
  template <typename F, typename S>
  ostream& operator<<(ostream& os, const map<F, S>& v) {
    os << "[";
    typename map<F, S>::const_iterator it;
    for (it = v.begin(); it != v.end(); it++) {
      if (it != v.begin()) os << ", ";
      os << it->first << " = " << it->second;
    }
    return os << "]";
  }
  template <typename F, typename S>
  ostream& operator<<(ostream& os, const unordered_map<F, S>& v) {
    os << "[";
    typename unordered_map<F, S>::const_iterator it;
    for (it = v.begin(); it != v.end(); it++) {
      if (it != v.begin()) os << ", ";
      os << it->first << " = " << it->second;
    }
    return os << "]";
  }
  template <typename... T>
  void read(T&... args) {
    ((cin >> args), ...);
  }
  template <typename... T>
  void write(T&&... args) {
    ((cout << args << " "), ...);
  }
  inline void file_io(string path1 = "", string path2 = "") {
    if (path2.size() == 0) path2 = path1;
    freopen(path1.c_str(), "r", stdin);
    freopen(path2.c_str(), "w", stdout);
  }
  template <typename T>
  T egcd(T a, T b, T& x, T& y) {
    x = 1, y = 0;
    T x1 = 0, y1 = 1, a1 = a, b1 = b;
    while (b1) {
      T q = a1 / b1;
      tie(x, x1) = make_tuple(x1, x - q * x1);
      tie(y, y1) = make_tuple(y1, y - q * y1);
      tie(a1, b1) = make_tuple(b1, a1 - q * b1);
    }
    return a1;
  }
  template <typename F, typename S>
  F bigMod(F a, F b, S mod) {
    a %= mod;
    F res = 1;
    while (b > 0) {
      if (b & 1) res = ((long long)res * a) % mod;
      a = ((long long)a * a) % mod;
      b >>= 1;
    }
    return res;
  }
  inline int modAdd(long long _a, long long _b, long long mod) {
    if (_a < 0) {
      _a += mod;
    }
    if (_b < 0) {
      _b += mod;
    }
    if (_a + _b >= mod) return (_a + _b - mod);
    return (_a + _b);
  }
  inline int modMul(long long _a, long long _b, long long mod) {
    if (_a < 0) {
      _a += mod;
    }
    if (_b < 0) {
      _b += mod;
    }
    return (_a * _b) % mod;
  }
  inline int modInv(long long a, long long mod) {
    return bigMod(a, mod - 2, mod);
  }
  const long long mod = 998244353;
  int solve() {
    int n;
    cin >> n;
    int dp[n + 5][2], ans = 0;
    memset(dp, 0, sizeof dp);
    dp[0][0] = 1;
    for (int i = 0; i < n; i++) {
      int val;
      cin >> val;
      dp[val + 1][0] = modAdd(dp[val + 1][0], dp[val + 1][0], mod);
      dp[val + 1][0] = modAdd(dp[val + 1][0], dp[val][0], mod);
      if (val - 1 >= 0)
        dp[val - 1][1] = modAdd(dp[val - 1][1], dp[val - 1][1], mod);
      if (val - 1 >= 0)
        dp[val - 1][1] = modAdd(dp[val - 1][1], dp[val - 1][0], mod);
      dp[val + 1][1] = modAdd(dp[val + 1][1], dp[val + 1][1], mod);
    }
    for (int i = 0; i < n + 5; i++) {
      ans = modAdd(ans, dp[i][0], mod);
      ans = modAdd(ans, dp[i][1], mod);
    }
    ans = modAdd(ans, -1, mod);
    cout << ans << "\n";
    return 0;
  }
  int main() {
    ios::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
    ;
    ;
    int t = 1, cs = 0;
    cin >> t;
    while (t--) {
      solve();
    }
    return 0;
  }
  