description: Consider the insertion sort algorithm used to sort an integer sequence [a_1, a_2, …, a_n] of length n in non-decreasing order.
  
  For each i in order from 2 to n, do the following. If a_i ≥ a_{i-1}, do nothing and move on to the next value of i. Otherwise, find the smallest j such that a_i < a_j, shift the elements on positions from j to i-1 by one position to the right, and write down the initial value of a_i to position j. In this case we'll say that we performed an insertion of an element from position i to position j.
  
  It can be noticed that after processing any i, the prefix of the sequence [a_1, a_2, …, a_i] is sorted in non-decreasing order, therefore, the algorithm indeed sorts any sequence.
  
  For example, sorting [4, 5, 3, 1, 3] proceeds as follows: 
  
    * i = 2: a_2 ≥ a_1, do nothing; 
    * i = 3: j = 1, insert from position 3 to position 1: [3, 4, 5, 1, 3]; 
    * i = 4: j = 1, insert from position 4 to position 1: [1, 3, 4, 5, 3]; 
    * i = 5: j = 3, insert from position 5 to position 3: [1, 3, 3, 4, 5]. 
  
  
  
  You are given an integer n and a list of m integer pairs (x_i, y_i). We are interested in sequences such that if you sort them using the above algorithm, exactly m insertions will be performed: first from position x_1 to position y_1, then from position x_2 to position y_2, ..., finally, from position x_m to position y_m.
  
  How many sequences of length n consisting of (not necessarily distinct) integers between 1 and n, inclusive, satisfy the above condition? Print this number modulo 998 244 353.
  
  Input
  
  Each test contains multiple test cases. The first line contains the number of test cases t (1 ≤ t ≤ 10^5). Description of the test cases follows.
  
  The first line of each test case contains two integers n and m (2 ≤ n ≤ 2 ⋅ 10^5; 0 ≤ m < n) — the length of the sequence and the number of insertions.
  
  The i-th of the following m lines contains two integers x_i and y_i (2 ≤ x_1 < x_2 < … < x_m ≤ n; 1 ≤ y_i < x_i). These lines describe the sequence of insertions in chronological order.
  
  It is guaranteed that the sum of m over all test cases does not exceed 2 ⋅ 10^5. Note that there is no constraint on the sum of n of the same kind.
  
  Output
  
  For each test case, print the number of sequences of length n consisting of integers from 1 to n such that sorting them with the described algorithm produces the given sequence of insertions, modulo 998 244 353.
  
  Example
  
  Input
  
  
  3
  3 0
  3 2
  2 1
  3 1
  5 3
  3 1
  4 1
  5 3
  
  
  Output
  
  
  10
  1
  21
  
  Note
  
  In the first test case, the algorithm performs no insertions — therefore, the initial sequence is already sorted in non-decreasing order. There are 10 such sequences: [1, 1, 1], [1, 1, 2], [1, 1, 3], [1, 2, 2], [1, 2, 3], [1, 3, 3], [2, 2, 2], [2, 2, 3], [2, 3, 3], [3, 3, 3].
  
  In the second test case, the only sequence satisfying the conditions is [3, 2, 1].
  
  In the third test case, [4, 5, 3, 1, 3] is one of the sought sequences.
solution: #include <bits/stdc++.h>
  using namespace std;
  const int INF = 0x3f3f3f3f;
  const long long INF64 = 0x3f3f3f3f3f3f3f3f;
  const double PI = acos(-1);
  typedef std::priority_queue<int, vector<int>, greater<int>> small_pq;
  typedef std::priority_queue<int, vector<int>, less<int>> big_pq;
  template <typename A, typename B>
  ostream &operator<<(ostream &os, const pair<A, B> &p) {
    return os << '(' << p.first << ", " << p.second << ')';
  }
  template <typename T_container, typename T = typename enable_if<
                                      !is_same<T_container, string>::value,
                                      typename T_container::value_type>::type>
  ostream &operator<<(ostream &os, const T_container &v) {
    os << '{';
    string sep;
    for (const T &x : v) os << sep << x, sep = ", ";
    return os << '}';
  }
  void dbg_out() {}
  template <typename Head, typename... Tail>
  void dbg_out(Head H, Tail... T) {
    cerr << " " << H;
    if (sizeof...(T) > 0) cerr << " ,";
    dbg_out(T...);
  }
  void dbg_name(const string &s) {
    string ss = s;
    replace(ss.begin(), ss.end(), ',', ' ');
    cerr << "  ( " << ss << " )  ";
  }
  template <typename T>
  inline void setmin(T &a, const T &b) {
    if (b < a) a = b;
  }
  template <typename T>
  inline void setmax(T &a, const T &b) {
    if (b > a) a = b;
  }
  struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
      x += 0x9e3779b97f4a7c15;
      x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
      x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
      return x ^ (x >> 31);
    }
    size_t operator()(uint64_t x) const {
      static const uint64_t FIXED_RANDOM =
          chrono::steady_clock::now().time_since_epoch().count();
      return splitmix64(x + FIXED_RANDOM);
    }
  };
  unordered_map<long long, int, custom_hash> safe_map;
  mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
  mt19937_64 rnd64(chrono::steady_clock::now().time_since_epoch().count());
  const int MOD = 998244353;
  int mul(int x, int y) { return 1ll * x * y % MOD; }
  int add(int x, int y) { return ((x + y) % MOD + MOD) % MOD; }
  int sub(int x, int y) { return ((x - y) % MOD + MOD) % MOD; }
  int qpow(int a, int b) {
    long long ans = 1;
    while (b) {
      if (b & 1) ans = mul(ans, a);
      a = mul(a, a);
      b /= 2;
    }
    return ans;
  }
  const int N = 6e5 + 5;
  struct BitTree {
    const static int R = N;
    int a[R];
    void add(int pos, int x) {
      while (pos < R) {
        a[pos] += x;
        pos += ((-(pos)) & (pos));
      }
    }
    int sum(int pos) {
      int ans = 0;
      while (pos) {
        ans += a[pos];
        pos -= ((-(pos)) & (pos));
      }
      return ans;
    }
    int kth(int k) {
      int now = 0;
      for (int i = 18; i >= 0; i--) {
        if (a[now + (1 << i)] < k) {
          k -= a[now + (1 << i)];
          now += 1 << i;
        }
      }
      return now + 1;
    }
  } bt;
  int fac[N], inv[N];
  int x[N], y[N];
  int C(int n, int m) {
    if (n < 0 || m < 0 || n < m) return 0;
    return mul(fac[n], mul(inv[m], inv[n - m]));
  }
  int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    fac[0] = 1;
    for (int(i) = int(1); int(i) <= int(N - 1); i++) fac[i] = mul(i, fac[i - 1]);
    inv[N - 1] = qpow(fac[N - 1], MOD - 2);
    for (int(i) = int(N - 2); int(i) >= int(0); i--)
      inv[i] = mul(inv[i + 1], i + 1);
    for (int(i) = int(1); int(i) <= int(N - 1); i++) bt.add(i, 1);
    int t;
    cin >> t;
    while (t--) {
      int n, m;
      cin >> n >> m;
      for (int(i) = int(1); int(i) <= int(m); i++) cin >> x[i] >> y[i];
      vector<int> pos(m + 1);
      int cnt = 0;
      for (int(i) = int(m); int(i) >= int(1); i--) {
        pos[i] = bt.kth(y[i]);
        if (bt.sum(pos[i] + 1) - bt.sum(pos[i])) cnt++;
        bt.add(pos[i], -1);
      }
      int ans = C(2 * n - 1 - cnt, n);
      cout << ans << endl;
      for (int(i) = int(1); int(i) <= int(m); i++) {
        bt.add(pos[i], 1);
      }
    }
    return 0;
  }
  