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 = 2e5 + 10, mod = 998244353;
  int sum[N << 2];
  void build(int p, int l, int r) {
    sum[p] = r - l + 1;
    if (l == r) return;
    int mid = (l + r) >> 1;
    build(p << 1, l, mid);
    build(p << 1 | 1, mid + 1, r);
  }
  int qry(int p, int l, int r, int k) {
    if (l == r) return l;
    int mid = (l + r) >> 1;
    if (k <= sum[p << 1])
      return qry(p << 1, l, mid, k);
    else
      return qry(p << 1 | 1, mid + 1, r, k - sum[p << 1]);
  }
  void add(int p, int l, int r, int x, int v) {
    sum[p] += v;
    if (l == r) return;
    int mid = (l + r) >> 1;
    if (x <= mid)
      add(p << 1, l, mid, x, v);
    else
      add(p << 1 | 1, mid + 1, r, x, v);
  }
  int x[N], y[N], t[N], fac[N * 2], inv[N * 2];
  set<int> S;
  int C(int n, int m) { return 1ll * fac[n] * inv[m] % mod * inv[n - m] % mod; }
  int qpow(int a, int b) {
    int ans = 1;
    while (b) {
      if (b & 1) ans = 1ll * ans * a % mod;
      a = 1ll * a * a % mod;
      b >>= 1;
    }
    return ans;
  }
  int main() {
    int T, n, m, N = ::N - 10;
    scanf("%d", &T);
    build(1, 1, N);
    fac[0] = 1;
    for (int i = 1; i <= 2 * N; i++) fac[i] = 1ll * fac[i - 1] * i % mod;
    inv[2 * N] = qpow(fac[2 * N], mod - 2);
    for (int i = 2 * N; i >= 1; i--) inv[i - 1] = 1ll * inv[i] * i % mod;
    while (T--) {
      scanf("%d%d", &n, &m);
      S.clear();
      for (int i = 1; i <= m; i++) scanf("%d%d", x + i, y + i);
      for (int i = m; i >= 1; i--) {
        int p = qry(1, 1, N, y[i]), q = qry(1, 1, N, y[i] + 1);
        S.insert(q);
        add(1, 1, N, p, -1);
        t[i] = p;
      }
      for (int i = 1; i <= m; i++) add(1, 1, N, t[i], 1);
      printf("%d\n", C(2 * n - S.size() - 1, n));
    }
    return 0;
  }
  