Problem p02549 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vint = vector<int>;
using vvint = vector<vint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vchar = vector<char>;
using vvchar = vector<vchar>;
using vp = vector<P>;
using vpp = vector<pair<P, P>>;
using vvp = vector<vp>;

#define rep(i, n) for (int i = 0; i < n; ++i)
#pragma region Debug
istream &operator>>(istream &is, P &a) { return is >> a.first >> a.second; }
ostream &operator<<(ostream &os, const P &a) {
  return os << "(" << a.first << "," << a.second << ")";
}

template <typename T> void view(const std::vector<T> &v) {
  for (const auto &e : v) {
    std::cout << e << " ";
  }
  std::cout << std::endl;
}
template <typename T> void view(const std::vector<std::vector<T>> &vv) {
  for (const auto &v : vv) {
    view(v);
  }
}
#pragma endregion

#pragma region mod
const int p = 998244353;
struct mint {
  ll x;
  mint(ll xx = 0) : x(xx % p) {}
  mint &operator+=(const mint a) {
    if ((x += a.x) >= p)
      x -= p;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += p - a.x) >= p)
      x -= p;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= p;
    return *this;
  }

  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }

  mint pow(ll t) const {
    mint r = 1;
    mint a = *this;
    while (true) {
      if (t & 1) {
        r *= a;
      }
      t >>= 1;
      if (t == 0)
        break;
      a *= a;
    }

    return r;
  }

  mint inv() const { return pow(p - 2); }

  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

struct comb {
  vector<mint> fact, invs;
  comb(int n) : fact(n + 1), invs(n + 1) {
    assert(n < p);

    fact[0] = 1;
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;

    invs[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      invs[i - 1] = invs[i] * i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * invs[n - k] * invs[k];
  }
};
#pragma endregion

using vmint = vector<mint>;
int main() {
  int n, k;
  cin >> n >> k;
  set<int> s;
  vp lr(k);
  rep(i, k) {
    int l, r;
    cin >> l >> r;
    lr[i] = P(l, r);
  }

  vmint dp(n + 1, 0), cs(n + 1);
  cs[0] = 1;
  dp[1] = -1;

  for (int i = 0; i < n; i++) {
    for (int j = 0; j < k; ++j) {
      P p = lr[j];
      int l = p.first, r = p.second;
      if (i + l <= n) {
        dp[i + l] += cs[i];
      }
      if (i + r + 1 <= n) {
        dp[i + r + 1] -= cs[i];
      }
    }

    cs[i + 1] = cs[i] + dp[i + 1];
  }

  cout << cs[n - 1] << endl;
  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vint = vector<int>;
using vvint = vector<vint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vchar = vector<char>;
using vvchar = vector<vchar>;
using vp = vector<P>;
using vpp = vector<pair<P, P>>;
using vvp = vector<vp>;

#define rep(i, n) for (int i = 0; i < n; ++i)
#pragma region Debug
istream &operator>>(istream &is, P &a) { return is >> a.first >> a.second; }
ostream &operator<<(ostream &os, const P &a) {
  return os << "(" << a.first << "," << a.second << ")";
}

template <typename T> void view(const std::vector<T> &v) {
  for (const auto &e : v) {
    std::cout << e << " ";
  }
  std::cout << std::endl;
}
template <typename T> void view(const std::vector<std::vector<T>> &vv) {
  for (const auto &v : vv) {
    view(v);
  }
}
#pragma endregion

#pragma region mod
const int p = 998244353;
struct mint {
  ll x;
  mint(ll xx = 0) : x(xx % p) {}
  mint &operator+=(const mint a) {
    if ((x += a.x) >= p)
      x -= p;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += p - a.x) >= p)
      x -= p;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= p;
    return *this;
  }

  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }

  mint pow(ll t) const {
    mint r = 1;
    mint a = *this;
    while (true) {
      if (t & 1) {
        r *= a;
      }
      t >>= 1;
      if (t == 0)
        break;
      a *= a;
    }

    return r;
  }

  mint inv() const { return pow(p - 2); }

  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
};
istream &operator>>(istream &is, mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

struct comb {
  vector<mint> fact, invs;
  comb(int n) : fact(n + 1), invs(n + 1) {
    assert(n < p);

    fact[0] = 1;
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;

    invs[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      invs[i - 1] = invs[i] * i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * invs[n - k] * invs[k];
  }
};
#pragma endregion

using vmint = vector<mint>;
int main() {
  int n, k;
  cin >> n >> k;
  set<int> s;
  vp lr(k);
  rep(i, k) {
    int l, r;
    cin >> l >> r;
    lr[i] = P(l, r);
  }

  vmint dp(n);
  dp[0] = 1;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < k; ++j) {
      P p = lr[j];
      int l = p.first, r = p.second;
      for (int m = l; m <= r; ++m) {
        if (i + m < n) {
          dp[i + m] += dp[i];
        }
      }
    }
  }

  cout << dp[n - 1] << endl;
  return 0;
}