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;
  int read() {
    char c = getchar();
    int s = 0;
    int x = 1;
    while (c < '0' || c > '9') {
      if (c == '-') x = -1;
      c = getchar();
    }
    while (c >= '0' && c <= '9') {
      s = s * 10 + c - '0';
      c = getchar();
    }
    return s * x;
  }
  const int N = 2e5 + 55;
  const int mod = 998244353;
  int T, n, m, x, y, cd[N], cy[N], fac[N * 2], ifac[N * 2], st[N], top;
  int pd[N], ans;
  int summ[N * 4];
  int ksm(int x, int k) {
    int base = 1;
    while (k) {
      if (k & 1) base = 1ll * base * x % mod;
      k >>= 1;
      x = 1ll * x * x % mod;
    }
    return base;
  }
  int C(int n, int m) {
    if (n < m) return 0;
    return 1ll * fac[n] * ifac[m] % mod * ifac[n - m] % mod;
  }
  void add(int u, int l, int r, int x, int k) {
    if (l == r) {
      summ[u] += k;
      return;
    }
    if (x <= ((l + r) >> 1))
      add((u << 1), l, ((l + r) >> 1), x, k);
    else
      add((u << 1 | 1), ((l + r) >> 1) + 1, r, x, k);
    summ[u] = summ[(u << 1)] + summ[(u << 1 | 1)];
  }
  int ask(int u, int l, int r, int x) {
    if (l == r) return l;
    if (summ[(u << 1)] >= x)
      return ask((u << 1), l, ((l + r) >> 1), x);
    else
      return ask((u << 1 | 1), ((l + r) >> 1) + 1, r, x - summ[(u << 1)]);
  }
  void build(int u, int l, int r) {
    if (l == r) {
      summ[u] = 1;
      return;
    }
    build((u << 1), l, ((l + r) >> 1));
    build((u << 1 | 1), ((l + r) >> 1) + 1, r);
    summ[u] = summ[(u << 1)] + summ[(u << 1 | 1)];
  }
  void clear(int u, int l, int r) {
    summ[u] = 0;
    if (l == r) {
      pd[l] = 0;
      return;
    }
    clear((u << 1), l, ((l + r) >> 1));
    clear((u << 1 | 1), ((l + r) >> 1) + 1, r);
  }
  void solve() {
    ans = 0;
    map<int, int> ma;
    for (int i = m; i >= 1; i--) {
      x = ask(1, 1, N - 55, cd[i]);
      y = ask(1, 1, N - 55, cd[i] + 1);
      add(1, 1, N - 55, x, -1);
      st[++top] = x;
      if (!ma[y]) ans++;
      ma[y] = 1;
    }
    for (int i = 1; i <= top; i++) add(1, 1, N - 55, st[i], 1);
    top = 0;
    cout << C(2 * n - 1 - ans, n) << '\n';
  }
  int main() {
    fac[0] = ifac[0] = 1;
    for (int i = 1; i <= N * 2 - 5; i++) fac[i] = 1ll * fac[i - 1] * i % mod;
    ifac[N * 2 - 5] = ksm(fac[N * 2 - 5], mod - 2);
    for (int i = N * 2 - 6; i >= 1; i--)
      ifac[i] = 1ll * ifac[i + 1] * (i + 1) % mod;
    build(1, 1, N - 55);
    cin >> T;
    while (T--) {
      n = read();
      m = read();
      for (int i = 1; i <= m; i++) x = read(), y = read(), cd[i] = y;
      solve();
    }
    return 0;
  }
  