Problem p03861 (C++)

Buggy submission (status: Time Limit Exceeded):
#pragma region header
#include <bits/stdc++.h>
using namespace std;

#define CPP_CAT(x, y) CPP_CAT_I(x, y)
#define CPP_CAT_I(x, y) x##y
// #define CPP_STR(x) CPP_STR_I(x)
// #define CPP_STR_I(args...) #args
// #define ASSERT(expr...) assert((expr))

using i8 = int8_t;
using u8 = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
using f32 = float;
using f64 = double;
// using f80 = __float80;

constexpr i64 INF = 1'010'000'000'000'000'017LL;
constexpr i64 MOD = 1'000'000'007LL;
constexpr f64 EPS = 1e-12;
constexpr f64 PI = 3.14159265358979323846;
constexpr char EL[] = "\n";

#define FOR(i, start, end)                                                     \
  for (i64 i = (start), CPP_CAT(i, xxxx_end) = (end);                          \
       i < CPP_CAT(i, xxxx_end); ++i)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define ALL(f, c, ...)                                                         \
  (([&](decltype((c)) cccc) {                                                  \
    return (f)(std::begin(cccc), std::end(cccc), ##__VA_ARGS__);               \
  })(c))
#define UNIQUE(x) (x).erase(unique(all(x)), (x).end());
#define REPIT(x) for (auto it = (x).begin(), end = (x).end(); it != end; ++it)
#define perm(c)                                                                \
  sort(all(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(all(c)))

template <typename T = i64> T IN() {
  T x;
  cin >> x;
  return (x);
}

template <typename C> i64 SIZE(const C &c) {
  return static_cast<i64>(c.size());
}
template <typename T, size_t N> i64 SIZE(const T (&)[N]) {
  return static_cast<i64>(N);
}

template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

void print() { cout << EL; }
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail) != 0)
    cout << " ";
  print(forward<Tail>(tail)...);
}
template <class T> void print(vector<T> &vec) {
  for (auto &a : vec) {
    cout << a;
    if (&a != &vec.back())
      cout << " ";
  }
  cout << EL;
}
template <class T> void print(vector<vector<T>> &df) {
  for (auto &vec : df) {
    print(vec);
  }
}

struct ProconInit {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;

  ProconInit() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} PROCON_INIT;
#pragma endregion

signed solve() {
  i64 a, b, x;
  cin >> a >> b >> x;
  i64 ans = 0;
  for (i64 i = a; i <= b; ++i) {
    if (i % x == 0)
      ans++;
  }
  print(ans);
  return 0;
}

#ifndef LOCALCODE
signed main() { return solve(); }
#endif


Fixed submission:
#pragma region header
#include <bits/stdc++.h>
using namespace std;

#define CPP_CAT(x, y) CPP_CAT_I(x, y)
#define CPP_CAT_I(x, y) x##y
// #define CPP_STR(x) CPP_STR_I(x)
// #define CPP_STR_I(args...) #args
// #define ASSERT(expr...) assert((expr))

using i8 = int8_t;
using u8 = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
using f32 = float;
using f64 = double;
// using f80 = __float80;

constexpr i64 INF = 1'010'000'000'000'000'017LL;
constexpr i64 MOD = 1'000'000'007LL;
constexpr f64 EPS = 1e-12;
constexpr f64 PI = 3.14159265358979323846;
constexpr char EL[] = "\n";

#define FOR(i, start, end)                                                     \
  for (i64 i = (start), CPP_CAT(i, xxxx_end) = (end);                          \
       i < CPP_CAT(i, xxxx_end); ++i)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define ALL(f, c, ...)                                                         \
  (([&](decltype((c)) cccc) {                                                  \
    return (f)(std::begin(cccc), std::end(cccc), ##__VA_ARGS__);               \
  })(c))
#define UNIQUE(x) (x).erase(unique(all(x)), (x).end());
#define REPIT(x) for (auto it = (x).begin(), end = (x).end(); it != end; ++it)
#define perm(c)                                                                \
  sort(all(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(all(c)))

template <typename T = i64> T IN() {
  T x;
  cin >> x;
  return (x);
}

template <typename C> i64 SIZE(const C &c) {
  return static_cast<i64>(c.size());
}
template <typename T, size_t N> i64 SIZE(const T (&)[N]) {
  return static_cast<i64>(N);
}

template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

void print() { cout << EL; }
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail) != 0)
    cout << " ";
  print(forward<Tail>(tail)...);
}
template <class T> void print(vector<T> &vec) {
  for (auto &a : vec) {
    cout << a;
    if (&a != &vec.back())
      cout << " ";
  }
  cout << EL;
}
template <class T> void print(vector<vector<T>> &df) {
  for (auto &vec : df) {
    print(vec);
  }
}

struct ProconInit {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;

  ProconInit() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} PROCON_INIT;
#pragma endregion

signed solve() {
  i64 a, b, x;
  cin >> a >> b >> x;
  i64 div_a = a % x == 0 ? a / x - 1 : a / x;
  i64 div_b = b / x;
  print(div_b - div_a);
  return 0;
}

#ifndef LOCALCODE
signed main() { return solve(); }
#endif