Problem p02549 (C++)

Buggy submission (status: Runtime Error):
// {{{ by unolight
#pragma region
#include <bits/stdc++.h>
#include <unistd.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#pragma GCC diagnostic ignored "-Wunused-function"
#define SZ(x) ((int)(x).size())
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define REP(i, n) for (int i = 0; i < int(n); i++)
#define REP1(i, a, b) for (int i = (a); i <= int(b); i++)
#define MP make_pair
#define PB push_back
using namespace std;
typedef int64_t LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

namespace {
namespace unolight {
// Read Input
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" PRId64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
// Write Output
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f\n", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}

#ifdef UNOLIGHT
#include "dump.hpp"
#else
#define dump(...)
#endif

template <class T> inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T> using MaxHeap = priority_queue<T>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <class T, class F = less<T>> void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
#pragma endregion
// }}}

// {{{ ModInt
template <int _MOD> struct ModInt {
  static const auto MOD = _MOD;
  template <class T>
  using integral_only = typename enable_if<is_integral<T>::value>::type;

  int x;
  constexpr ModInt() : x() {}

  template <class T, integral_only<T> * = nullptr> ModInt(T _x = 0) {
    x = _x % MOD;
    if (x < 0)
      x += MOD;
  }
  ModInt operator-() const { return {x == 0 ? 0 : MOD - x}; }
  ModInt &operator+=(const ModInt a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt a) {
    x = (long long)x * a.x % MOD;
    return *this;
  }
  ModInt &operator/=(const ModInt a) { return (*this) *= a.inv(); }

  ModInt operator+(const ModInt a) const { return ModInt(*this) += a; }
  ModInt operator-(const ModInt a) const { return ModInt(*this) -= a; }
  ModInt operator*(const ModInt a) const { return ModInt(*this) *= a; }
  ModInt operator/(const ModInt a) const { return ModInt(*this) /= a; }
  ModInt inv() const {
    // for prime MOD
    return pow(MOD - 2);
  }
  ModInt inv2() const {
    // work for non-prime MOD if gcd(x,MOD) = 1
    int a = x, b = MOD, u = 1, v = 0;
    while (b != 0) {
      int t = a / b;
      a -= t * b;
      u -= t * v;
      swap(a, b);
      swap(u, v);
    }
    return u;
  }
  template <class T, integral_only<T> * = nullptr> ModInt pow(T t) const {
    ModInt r = 1, p = *this;
    while (t) {
      if (t & 1)
        r *= p;
      p *= p;
      t >>= 1;
    }
    return r;
  }

  bool operator==(ModInt rhs) const { return x == rhs.x; }
  bool operator!=(ModInt rhs) const { return x != rhs.x; }
  bool operator<(ModInt rhs) const { return x < rhs.x; }
  bool operator<=(ModInt rhs) const { return x <= rhs.x; }
  bool operator>(ModInt rhs) const { return x > rhs.x; }
  bool operator>=(ModInt rhs) const { return x >= rhs.x; }

  friend string to_string(ModInt i) { return to_string(i.x); }
  friend istream &operator>>(istream &i, ModInt &a) { return i >> a.x; }
  friend ostream &operator<<(ostream &o, const ModInt &a) { return o << a.x; }
};

const int MOD = 998244353;
using mint = ModInt<MOD>;
// }}}

void main() {
  int n, k;
  R(n, k);
  vector<mint> dp(n * 2, 0);
  vector<PII> a(k);
  for (int i = 0; i < k; i++) {
    R(a[i].first, a[i].second);
  }
  dp[0] = 1;
  mint sum = 0;
  for (int i = 0; i < n; i++) {
    // if ( dp[i]==0 ) continue;
    sum += dp[i];
    for (int j = 0; j < k; j++) {
      int l = a[j].first, r = a[j].second;
      dp[i + l] += sum;
      dp[i + r + 1] -= sum;
    }
    // W(dp);
  }
  W(dp[n - 1]);
}

} // namespace unolight
} // namespace
int main() {
  unolight::main();
  return 0;
}
// }}}


Fixed submission:
// {{{ by unolight
#pragma region
#include <bits/stdc++.h>
#include <unistd.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#pragma GCC diagnostic ignored "-Wunused-function"
#define SZ(x) ((int)(x).size())
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define REP(i, n) for (int i = 0; i < int(n); i++)
#define REP1(i, a, b) for (int i = (a); i <= int(b); i++)
#define MP make_pair
#define PB push_back
using namespace std;
typedef int64_t LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

namespace {
namespace unolight {
// Read Input
template <class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" PRId64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U> void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
// Write Output
template <class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f\n", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T> void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin())
      putchar(' ');
}
void W() {}
template <class T, class... U> void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}

#ifdef UNOLIGHT
#include "dump.hpp"
#else
#define dump(...)
#endif

template <class T> inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T> inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T> using MaxHeap = priority_queue<T>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <class T, class F = less<T>> void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
#pragma endregion
// }}}

// {{{ ModInt
template <int _MOD> struct ModInt {
  static const auto MOD = _MOD;
  template <class T>
  using integral_only = typename enable_if<is_integral<T>::value>::type;

  int x;
  constexpr ModInt() : x() {}

  template <class T, integral_only<T> * = nullptr> ModInt(T _x = 0) {
    x = _x % MOD;
    if (x < 0)
      x += MOD;
  }
  ModInt operator-() const { return {x == 0 ? 0 : MOD - x}; }
  ModInt &operator+=(const ModInt a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt a) {
    x = (long long)x * a.x % MOD;
    return *this;
  }
  ModInt &operator/=(const ModInt a) { return (*this) *= a.inv(); }

  ModInt operator+(const ModInt a) const { return ModInt(*this) += a; }
  ModInt operator-(const ModInt a) const { return ModInt(*this) -= a; }
  ModInt operator*(const ModInt a) const { return ModInt(*this) *= a; }
  ModInt operator/(const ModInt a) const { return ModInt(*this) /= a; }
  ModInt inv() const {
    // for prime MOD
    return pow(MOD - 2);
  }
  ModInt inv2() const {
    // work for non-prime MOD if gcd(x,MOD) = 1
    int a = x, b = MOD, u = 1, v = 0;
    while (b != 0) {
      int t = a / b;
      a -= t * b;
      u -= t * v;
      swap(a, b);
      swap(u, v);
    }
    return u;
  }
  template <class T, integral_only<T> * = nullptr> ModInt pow(T t) const {
    ModInt r = 1, p = *this;
    while (t) {
      if (t & 1)
        r *= p;
      p *= p;
      t >>= 1;
    }
    return r;
  }

  bool operator==(ModInt rhs) const { return x == rhs.x; }
  bool operator!=(ModInt rhs) const { return x != rhs.x; }
  bool operator<(ModInt rhs) const { return x < rhs.x; }
  bool operator<=(ModInt rhs) const { return x <= rhs.x; }
  bool operator>(ModInt rhs) const { return x > rhs.x; }
  bool operator>=(ModInt rhs) const { return x >= rhs.x; }

  friend string to_string(ModInt i) { return to_string(i.x); }
  friend istream &operator>>(istream &i, ModInt &a) { return i >> a.x; }
  friend ostream &operator<<(ostream &o, const ModInt &a) { return o << a.x; }
};

const int MOD = 998244353;
using mint = ModInt<MOD>;
// }}}

void main() {
  int n, k;
  R(n, k);
  vector<mint> dp(n * 2, 0);
  vector<PII> a(k);
  for (int i = 0; i < k; i++) {
    R(a[i].first, a[i].second);
  }
  dp[0] = 1;
  mint sum = 0;
  for (int i = 0; i < n; i++) {
    // if ( dp[i]==0 ) continue;
    sum += dp[i];
    for (int j = 0; j < k; j++) {
      int l = a[j].first, r = a[j].second;
      if (i + l <= n)
        dp[i + l] += sum;
      if (i + r + 1 <= n)
        dp[i + r + 1] -= sum;
    }
    // W(dp);
  }
  W(dp[n - 1]);
}

} // namespace unolight
} // namespace
int main() {
  unolight::main();
  return 0;
}
// }}}