Problem p03037 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i)
#define reps(i, b, e)                                                          \
  for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e)                                                          \
  for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...)                                                         \
  Type __VA_ARGS__;                                                            \
  input(__VA_ARGS__)

constexpr size_t operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T> using MaxHeap = priority_queue<T, vector<T>, less<T>>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head &&head, Tail &&...tail) {
  cin >> head;
  input(forward<Tail>(tail)...);
}

template <class T> inline void input(vector<T> &vec) {
  for (auto &e : vec) {
    cin >> e;
  }
}

template <class T> inline void input(vector<vector<T>> &mat) {
  for (auto &vec : mat) {
    input(vec);
  }
}

inline void print() { cout << "\n"; }
template <class Head, class... Tail>
inline void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail)) {
    cout << " ";
  }
  print(forward<Tail>(tail)...);
}

template <class T>
inline ostream &operator<<(ostream &os, const vector<T> &vec) {
  static constexpr const char *delim[] = {" ", ""};
  for (const auto &e : vec) {
    os << e << delim[&e == &vec.back()];
  }
  return os;
}

template <class T> inline vector<T> makeVector(const T &initValue, size_t sz) {
  return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
  return vector<decltype(makeVector<T>(initValue, args...))>(
      sz, makeVector<T>(initValue, args...));
}

template <class Func> class FixPoint : Func {
public:
  explicit constexpr FixPoint(Func &&f) noexcept : Func(forward<Func>(f)) {}

  template <class... Args>
  constexpr decltype(auto) operator()(Args &&...args) const {
    return Func::operator()(*this, std::forward<Args>(args)...);
  }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func &&f) noexcept {
  return FixPoint<Func>{forward<Func>(f)};
}

template <class T> inline bool chmax(T &a, const T &b) noexcept {
  return b > a && (a = b, true);
}

template <class T> inline bool chmin(T &a, const T &b) noexcept {
  return b < a && (a = b, true);
}

template <class T> inline T diff(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
// End Header }}}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  var(size_t, N, M);

  vector<size_t> imos(N);
  rep(i, M) {
    var(size_t, L, R);
    L--, R--;
    imos[L]++, imos[R + 1]--;
  }

  size_t res = 0;
  rep(i, N) {
    if (i != 0) {
      imos[i] += imos[i - 1];
    }
    res += (imos[i] == M);
  }

  print(res);

  return 0;
}


Fixed submission:
#include "bits/stdc++.h"

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i)
#define reps(i, b, e)                                                          \
  for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e)                                                          \
  for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...)                                                         \
  Type __VA_ARGS__;                                                            \
  input(__VA_ARGS__)

constexpr size_t operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T> using MaxHeap = priority_queue<T, vector<T>, less<T>>;
template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head &&head, Tail &&...tail) {
  cin >> head;
  input(forward<Tail>(tail)...);
}

template <class T> inline void input(vector<T> &vec) {
  for (auto &e : vec) {
    cin >> e;
  }
}

template <class T> inline void input(vector<vector<T>> &mat) {
  for (auto &vec : mat) {
    input(vec);
  }
}

inline void print() { cout << "\n"; }
template <class Head, class... Tail>
inline void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail)) {
    cout << " ";
  }
  print(forward<Tail>(tail)...);
}

template <class T>
inline ostream &operator<<(ostream &os, const vector<T> &vec) {
  static constexpr const char *delim[] = {" ", ""};
  for (const auto &e : vec) {
    os << e << delim[&e == &vec.back()];
  }
  return os;
}

template <class T> inline vector<T> makeVector(const T &initValue, size_t sz) {
  return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
  return vector<decltype(makeVector<T>(initValue, args...))>(
      sz, makeVector<T>(initValue, args...));
}

template <class Func> class FixPoint : Func {
public:
  explicit constexpr FixPoint(Func &&f) noexcept : Func(forward<Func>(f)) {}

  template <class... Args>
  constexpr decltype(auto) operator()(Args &&...args) const {
    return Func::operator()(*this, std::forward<Args>(args)...);
  }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func &&f) noexcept {
  return FixPoint<Func>{forward<Func>(f)};
}

template <class T> inline bool chmax(T &a, const T &b) noexcept {
  return b > a && (a = b, true);
}

template <class T> inline bool chmin(T &a, const T &b) noexcept {
  return b < a && (a = b, true);
}

template <class T> inline T diff(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
// End Header }}}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  var(size_t, N, M);

  vector<size_t> imos(N + 1);
  rep(i, M) {
    var(size_t, L, R);
    L--, R--;
    imos[L]++, imos[R + 1]--;
  }

  size_t res = 0;
  rep(i, N) {
    if (i != 0) {
      imos[i] += imos[i - 1];
    }
    res += (imos[i] == M);
  }

  print(res);

  return 0;
}