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 N = 200000, C = 19, mod = 998244353;
  int add(int a, int b, int p = mod) { return a + b >= p ? a + b - p : a + b; }
  int sub(int a, int b, int p = mod) { return a - b < 0 ? a - b + p : a - b; }
  int mul(int a, int b, int p = mod) { return 1LL * a * b % p; }
  void sadd(int &a, int b, int p = mod) { a = add(a, b, p); }
  void ssub(int &a, int b, int p = mod) { a = sub(a, b, p); }
  void smul(int &a, int b, int p = mod) { a = mul(a, b, p); }
  int inv[N * 2 + 9], fac[N * 2 + 9], ifac[N * 2 + 9];
  void Get_inv() {
    inv[1] = 1;
    fac[0] = fac[1] = 1;
    ifac[0] = ifac[1] = 1;
    for (int i = 2; i <= N << 1; ++i) {
      inv[i] = mul(mod - mod / i, inv[mod % i]);
      fac[i] = mul(fac[i - 1], i);
      ifac[i] = mul(ifac[i - 1], inv[i]);
    }
  }
  int Get_c(int n, int m) {
    return n < m || m < 0 ? 0 : mul(fac[n], mul(ifac[m], ifac[n - m]));
  }
  int c[N + 9];
  void Add(int p, int v) {
    for (; p <= N; p += p & -p) c[p] += v;
  }
  int Query(int p) {
    int res = 0;
    for (; p; p -= p & -p) res += c[p];
    return res;
  }
  int Query_kth(int p) {
    int res = 0;
    for (int i = C - 1; i >= 0; --i)
      if (res + (1 << i) <= N && c[res + (1 << i)] < p) p -= c[res += 1 << i];
    return res + 1;
  }
  void Get_c() {
    for (int i = 1; i <= N; ++i) Add(i, 1);
  }
  void start() {
    Get_inv();
    Get_c();
  }
  int n, m, x[N + 9], y[N + 9];
  void into() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= m; ++i) scanf("%d%d", &x[i], &y[i]);
  }
  int ans;
  void Get_ans() {
    int cnt = 0;
    vector<int> tmp;
    for (int i = m; i >= 1; --i) {
      int p = Query_kth(y[i]);
      if (y[i] + 1 == Query(p + 1)) ++cnt;
      Add(p, -1);
      tmp.push_back(p);
    }
    for (int p : tmp) Add(p, 1);
    ans = Get_c(n * 2 - cnt - 1, n);
  }
  void work() { Get_ans(); }
  void outo() { printf("%d\n", ans); }
  int main() {
    int T = 1;
    scanf("%d", &T);
    start();
    for (; T--;) {
      into();
      work();
      outo();
    }
    return 0;
  }
  