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 M = 400005;
  const int MOD = 998244353;
  long long read() {
    long long x = 0, f = 1;
    char c;
    while ((c = getchar()) < '0' || c > '9') {
      if (c == '-') f = -1;
    }
    while (c >= '0' && c <= '9') {
      x = (x << 3) + (x << 1) + (c ^ 48);
      c = getchar();
    }
    return x * f;
  }
  long long T, n, m, fac[M], inv[M];
  void init(long long n) {
    fac[0] = inv[0] = inv[1] = 1;
    for (long long i = 1; i <= n; i++) fac[i] = fac[i - 1] * i % MOD;
    for (long long i = 2; i <= n; i++)
      inv[i] = inv[MOD % i] * (MOD - MOD / i) % MOD;
    for (long long i = 2; i <= n; i++) inv[i] = inv[i - 1] * inv[i] % MOD;
  }
  long long C(long long n, long long m) {
    if (n < m || m < 0) return 0;
    return fac[n] * inv[m] % MOD * inv[n - m] % MOD;
  }
  namespace treap {
  long long rt, cnt, ch[M][2], val[M], hp[M], tg[M];
  void clear() {
    for (long long i = 1; i <= cnt; i++) ch[i][0] = ch[i][1] = val[i] = tg[i] = 0;
    rt = cnt = 0;
  }
  struct node {
    long long p[2];
    node() { p[0] = p[1] = 0; }
  } emp;
  void add(long long x, long long v) {
    if (!x) return;
    val[x] += v;
    tg[x] += v;
  }
  void down(long long x) {
    if (!tg[x]) return;
    add(ch[x][0], tg[x]);
    add(ch[x][1], tg[x]);
    tg[x] = 0;
  }
  node split(long long x, long long v) {
    if (!x) return emp;
    long long d = val[x] <= v;
    down(x);
    node y = split(ch[x][d], v);
    ch[x][d] = y.p[d ^ 1];
    y.p[d ^ 1] = x;
    return y;
  }
  long long merge(long long x, long long y) {
    if (!x || !y) return x + y;
    if (hp[x] < hp[y]) {
      down(x);
      ch[x][1] = merge(ch[x][1], y);
      return x;
    }
    down(y);
    ch[y][0] = merge(x, ch[y][0]);
    return y;
  }
  long long get(long long x) {
    cnt++;
    val[cnt] = x;
    hp[cnt] = rand();
    return cnt;
  }
  long long find(long long x) {
    node t = split(rt, x - 1), w = split(t.p[1], x);
    if (w.p[0] > 0) {
      add(w.p[0], 1);
      add(w.p[1], 1);
      rt = merge(t.p[0], merge(w.p[0], w.p[1]));
      return 0;
    }
    w.p[0] = merge(get(x), w.p[1]);
    add(w.p[0], 1);
    rt = merge(t.p[0], w.p[0]);
    return 1;
  }
  }  // namespace treap
  signed main() {
    T = read();
    init(4e5);
    while (T--) {
      n = read();
      m = read();
      treap::clear();
      long long ans = 0;
      for (long long i = 1; i <= m; i++) {
        long long a = read(), b = read();
        if (treap::find(b)) ans++;
      }
      printf("%lld\n", C(2 * n - ans - 1, n));
    }
  }
  