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

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#include <iostream>
using namespace std;

#define int long long int
#define all(x) (x).begin(), (x).end()
#define removeDuplicates(a) a.resize(unique(all(a)) - a.begin())
#define endl '\\n'

const int mod = 998244353;

class segtree {
  int sz;
  vector<int> adds;
  vector<int> cnt;

public:
  segtree(int n) {
    sz = 1;
    while (sz < n) {
      sz = sz * 2;
    }
    adds.assign(2 * sz, 0LL);
    cnt.assign(2 * sz, 0LL);
  }
  void make(int l, int r, int v, int start, int left, int right) {
    if (left >= r || right <= l) {
      return;
    }
    if (left >= l && right <= r) {
      adds[start] = (adds[start] + v) % mod;
      return;
    }
    int mid = (left + right) / 2;
    make(l, r, v, 2 * start + 1, left, mid);
    make(l, r, v, 2 * start + 2, mid, right);
  }
  void make(int l, int r, int v) { make(l, r, v, 0, 0, sz); }
  int val(int i, int v, int start, int left, int right) {
    if (right - left == 1) {
      return (v + adds[start]) % mod;
    }
    int mid = (left + right) / 2;
    int num = (v + adds[start]) % mod;
    if (i < mid) {
      return val(i, num, 2 * start + 1, left, mid) % mod;
    } else {
      return val(i, num, 2 * start + 2, mid, right) % mod;
    }
  }
  int val(int i) { return val(i, 0, 0, 0, sz) % mod; }
};

void solve() {
  int n, k;
  cin >> n >> k;
  segtree st(n);
  vector<pair<int, int>> ranges;
  for (int j = 0; j < k; j++) {
    int u, v;
    cin >> u >> v;
    u--;
    ranges.push_back({u, v});
  }
  sort(all(ranges));
  for (pair<int, int> p : ranges) {
    st.make(p.first + 1, min(p.second + 1, n), 1);
  }
  for (int i = 1; i < n; i++) {
    int a = st.val(i);
    for (pair<int, int> p : ranges) {
      st.make(p.first + i + 1, min(p.second + i + 1, n), a);
    }
  }
  cout << st.val(n - 1) << endl;
}

int32_t main() {

  // remove for interactive problems
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  solve();
  cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\\n";

  return 0;
}

Error: TLE

Fixed submission:

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#include <iostream>
using namespace std;

// #define int long long int
#define all(x) (x).begin(), (x).end()
#define removeDuplicates(a) a.resize(unique(all(a)) - a.begin())
#define endl '\\n'

template <typename T> T inverse(T a, T m) {
  T u = 0, v = 1;
  while (a != 0) {
    T t = m / a;
    m -= t * a;
    swap(a, m);
    u -= t * v;
    swap(u, v);
  }
  assert(m == 1);
  return u;
}

template <typename T> class Modular {
public:
  using Type = typename decay<decltype(T::value)>::type;

  constexpr Modular() : value() {}
  template <typename U> Modular(const U &x) { value = normalize(x); }

  template <typename U> static Type normalize(const U &x) {
    Type v;
    if (-mod() <= x && x < mod())
      v = static_cast<Type>(x);
    else
      v = static_cast<Type>(x % mod());
    if (v < 0)
      v += mod();
    return v;
  }

  const Type &operator()() const { return value; }
  template <typename U> explicit operator U() const {
    return static_cast<U>(value);
  }
  constexpr static Type mod() { return T::value; }

  Modular &operator+=(const Modular &other) {
    if ((value += other.value) >= mod())
      value -= mod();
    return *this;
  }
  Modular &operator-=(const Modular &other) {
    if ((value -= other.value) < 0)
      value += mod();
    return *this;
  }
  template <typename U> Modular &operator+=(const U &other) {
    return *this += Modular(other);
  }
  template <typename U> Modular &operator-=(const U &other) {
    return *this -= Modular(other);
  }
  Modular &operator++() { return *this += 1; }
  Modular &operator--() { return *this -= 1; }
  Modular operator++(int) {
    Modular result(*this);
    *this += 1;
    return result;
  }
  Modular operator--(int) {
    Modular result(*this);
    *this -= 1;
    return result;
  }
  Modular operator-() const { return Modular(-value); }

  template <typename U = T>
  typename enable_if<is_same<typename Modular<U>::Type, int>::value,
                     Modular>::type &
  operator*=(const Modular &rhs) {
#ifdef _WIN32
    uint64_t x = static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value);
    uint32_t xh = static_cast<uint32_t>(x >> 32), xl = static_cast<uint32_t>(x),
             d, m;
    asm("divl %4; \\n\\t" : "=a"(d), "=d"(m) : "d"(xh), "a"(xl), "r"(mod()));
    value = m;
#else
    value = normalize(static_cast<int64_t>(value) *
                      static_cast<int64_t>(rhs.value));
#endif
    return *this;
  }
  template <typename U = T>
  typename enable_if<is_same<typename Modular<U>::Type, int64_t>::value,
                     Modular>::type &
  operator*=(const Modular &rhs) {
    int64_t q = static_cast<int64_t>(static_cast<long double>(value) *
                                     rhs.value / mod());
    value = normalize(value * rhs.value - q * mod());
    return *this;
  }
  template <typename U = T>
  typename enable_if<!is_integral<typename Modular<U>::Type>::value,
                     Modular>::type &
  operator*=(const Modular &rhs) {
    value = normalize(value * rhs.value);
    return *this;
  }

  Modular &operator/=(const Modular &other) {
    return *this *= Modular(inverse(other.value, mod()));
  }

  template <typename U> friend const Modular<U> &abs(const Modular<U> &v) {
    return v;
  }

  template <typename U>
  friend bool operator==(const Modular<U> &lhs, const Modular<U> &rhs);

  template <typename U>
  friend bool operator<(const Modular<U> &lhs, const Modular<U> &rhs);

  template <typename U>
  friend std::istream &operator>>(std::istream &stream, Modular<U> &number);

private:
  Type value;
};

template <typename T>
bool operator==(const Modular<T> &lhs, const Modular<T> &rhs) {
  return lhs.value == rhs.value;
}
template <typename T, typename U>
bool operator==(const Modular<T> &lhs, U rhs) {
  return lhs == Modular<T>(rhs);
}
template <typename T, typename U>
bool operator==(U lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) == rhs;
}

template <typename T>
bool operator!=(const Modular<T> &lhs, const Modular<T> &rhs) {
  return !(lhs == rhs);
}
template <typename T, typename U>
bool operator!=(const Modular<T> &lhs, U rhs) {
  return !(lhs == rhs);
}
template <typename T, typename U>
bool operator!=(U lhs, const Modular<T> &rhs) {
  return !(lhs == rhs);
}

template <typename T>
bool operator<(const Modular<T> &lhs, const Modular<T> &rhs) {
  return lhs.value < rhs.value;
}

template <typename T>
Modular<T> operator+(const Modular<T> &lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) += rhs;
}
template <typename T, typename U>
Modular<T> operator+(const Modular<T> &lhs, U rhs) {
  return Modular<T>(lhs) += rhs;
}
template <typename T, typename U>
Modular<T> operator+(U lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) += rhs;
}

template <typename T>
Modular<T> operator-(const Modular<T> &lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) -= rhs;
}
template <typename T, typename U>
Modular<T> operator-(const Modular<T> &lhs, U rhs) {
  return Modular<T>(lhs) -= rhs;
}
template <typename T, typename U>
Modular<T> operator-(U lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) -= rhs;
}

template <typename T>
Modular<T> operator*(const Modular<T> &lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) *= rhs;
}
template <typename T, typename U>
Modular<T> operator*(const Modular<T> &lhs, U rhs) {
  return Modular<T>(lhs) *= rhs;
}
template <typename T, typename U>
Modular<T> operator*(U lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) *= rhs;
}

template <typename T>
Modular<T> operator/(const Modular<T> &lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) /= rhs;
}
template <typename T, typename U>
Modular<T> operator/(const Modular<T> &lhs, U rhs) {
  return Modular<T>(lhs) /= rhs;
}
template <typename T, typename U>
Modular<T> operator/(U lhs, const Modular<T> &rhs) {
  return Modular<T>(lhs) /= rhs;
}

template <typename T, typename U>
Modular<T> power(const Modular<T> &a, const U &b) {
  assert(b >= 0);
  Modular<T> x = a, res = 1;
  U p = b;
  while (p > 0) {
    if (p & 1)
      res *= x;
    x *= x;
    p >>= 1;
  }
  return res;
}

template <typename T> bool IsZero(const Modular<T> &number) {
  return number() == 0;
}

template <typename T> string to_string(const Modular<T> &number) {
  return to_string(number());
}

template <typename T>
std::ostream &operator<<(std::ostream &stream, const Modular<T> &number) {
  return stream << number();
}

template <typename T>
std::istream &operator>>(std::istream &stream, Modular<T> &number) {
  typename common_type<typename Modular<T>::Type, int64_t>::type x;
  stream >> x;
  number.value = Modular<T>::normalize(x);
  return stream;
}

/*
using ModType = int;

struct VarMod { static ModType value; };
ModType VarMod::value;
ModType& md = VarMod::value;
using Mint = Modular<VarMod>;
*/

constexpr int md = 998244353;
using Mint = Modular<std::integral_constant<decay<decltype(md)>::type, md>>;
// remember to comment out #define int long long int

vector<Mint> fact(1, 1);
vector<Mint> inv_fact(1, 1);

Mint C(int n, int k) {
  if (k < 0 || k > n) {
    return 0;
  }
  while ((int)fact.size() < n + 1) {
    fact.push_back(fact.back() * (int)fact.size());
    inv_fact.push_back(1 / fact.back());
  }
  return fact[n] * inv_fact[k] * inv_fact[n - k];
}

void solve() {
  int n, k;
  cin >> n >> k;
  vector<int> values;
  for (int i = 0; i < k; i++) {
    int u, v;
    cin >> u >> v;
    for (int j = u; j <= v; j++) {
      values.push_back(j);
    }
  }
  sort(all(values));
  vector<Mint> dp(n + 1);
  dp[1] = 1;
  for (int i = 1; i <= n; i++) {
    if (dp[i] == 0) {
      continue;
    }
    for (int d : values) {
      if (i + d > n) {
        break;
      }
      dp[i + d] += dp[i];
    }
  }
  cout << dp[n] << endl;
}

int32_t main() {

  // remove for interactive problems
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  solve();
  cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\\n";

  return 0;
}