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;
  long long read() {
    long long x = 0, f = 1;
    char c = getchar();
    while (c > '9' || c < '0') {
      if (c == '-') f = -1;
      c = getchar();
    }
    while (c >= '0' && c <= '9') {
      x = x * 10 + c - '0';
      c = getchar();
    }
    return f * x;
  }
  long long pow_mod(long long a, long long b) {
    long long ans = 1;
    while (b) {
      if (b & 1) ans = ans * a % 998244353;
      b >>= 1;
      a = a * a % 998244353;
    }
    return ans;
  }
  int n, m, T;
  long long ji[400032], invji[400032];
  struct TREE {
    int num;
  } tr[400032 << 3];
  vector<int> ve;
  struct ques {
    int x, y;
  } q[400032];
  long long C(int n, int m) {
    return ji[n] * invji[m] % 998244353 * invji[n - m] % 998244353;
  }
  void build(int rt, int l, int r) {
    tr[rt].num = r - l + 1;
    if (l == r) return;
    int mid = l + r >> 1;
    build(rt << 1, l, mid);
    build(rt << 1 | 1, mid + 1, r);
  }
  int query(int rt, int l, int r, int k) {
    if (l == r) return l;
    int mid = l + r >> 1;
    if (tr[rt << 1 | 1].num >= k)
      return query(rt << 1 | 1, mid + 1, r, k);
    else
      return query(rt << 1, l, mid, k - tr[rt << 1 | 1].num);
  }
  vector<int> cg;
  void change(int rt, int l, int r, int k) {
    if (l == r) {
      tr[rt].num = 0;
      cg.push_back(l);
      return;
    }
    int mid = l + r >> 1;
    if (tr[rt << 1 | 1].num >= k)
      change(rt << 1 | 1, mid + 1, r, k);
    else
      change(rt << 1, l, mid, k - tr[rt << 1 | 1].num);
    tr[rt].num = tr[rt << 1].num + tr[rt << 1 | 1].num;
  }
  void getback(int rt, int l, int r, int pos) {
    if (l == r) {
      tr[rt].num = 1;
      return;
    }
    int mid = l + r >> 1;
    if (pos <= mid)
      getback(rt << 1, l, mid, pos);
    else
      getback(rt << 1 | 1, mid + 1, r, pos);
    tr[rt].num = tr[rt << 1].num + tr[rt << 1 | 1].num;
  }
  bool vis[400032];
  int main() {
    T = read();
    ji[0] = 1;
    for (int i = 1; i < 400032; ++i) ji[i] = ji[i - 1] * i % 998244353;
    invji[400032 - 1] = pow_mod(ji[400032 - 1], 998244353 - 2);
    for (int i = 400032 - 2; i >= 0; --i)
      invji[i] = invji[i + 1] * (i + 1) % 998244353;
    build(1, 1, 200000);
    while (T--) {
      ve.clear();
      n = read(), m = read();
      for (int i = 1; i <= m; ++i) {
        q[i].x = read(), q[i].y = read();
      }
      int tmp = 200000 - n, lst = n;
      for (int i = m; i >= 1; --i) {
        tmp += lst - q[i].x;
        lst = q[i].x - 1;
        ve.push_back(query(1, 1, 200000, tmp + q[i].x - q[i].y));
        change(1, 1, 200000, tmp + q[i].x - q[i].y + 1);
      }
      int as = 0;
      for (int i = 0; i < ve.size(); ++i)
        if (!vis[ve[i]]) vis[ve[i]] = 1, as++;
      for (int i = 0; i < ve.size(); ++i) vis[ve[i]] = 0;
      cout << C(n + n - 1 - as, n) << '\n';
      for (int i = 0; i < cg.size(); ++i) getback(1, 1, 200000, cg[i]);
      cg.clear();
    }
    return 0;
  }
  