Problem p03708 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using ll = long long;
// using ll = boost::multiprecision::int128_t;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (ll i = int(m); i < int(n); ++i)
#define drep2(i, m, n) for (ll i = int(m) - 1; i >= int(n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) a.begin(), a.end()
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << " ";
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int Log2(ll x) {
  int k;
  for (k = 0; x > 0; ++k)
    x >>= 1;
  return k;
} // number of binary digits
const int INF = 1 << 30;
const ll INFll = 1ll << 62;
const ld EPS = 1e-10;
const ld PI = acos(-1.0);
const int MOD = int(1e9) + 7;

ll solve(ll a, ll b) {
  if (a == b)
    return 1;
  if (Log2(a) == Log2(b)) {
    a ^= (1 << (Log2(a) - 1));
    b ^= (1 << (Log2(b) - 1));
    return solve(a, b);
  }

  ll ans = 0;

  ll c = b;
  int d1 = Log2(b);
  c = b - (1ll << (d1 - 1));
  int d2 = Log2(c);
  c = (1ll << d2) - 1;
  c += (1ll << (d1 - 1));

  ans += c - a + 1;

  ll e = (1ll << (d1 - 1)) + a;
  ll f = (1ll << d1) - 1;
  if (c < e)
    ans += f - e + 1;
  else
    ans += f - c;

  return ans;
}

int main() {
  ll a, b;
  cin >> a >> b;
  cout << solve(a, b) << "\n";
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using ll = long long;
// using ll = boost::multiprecision::int128_t;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (ll i = int(m); i < int(n); ++i)
#define drep2(i, m, n) for (ll i = int(m) - 1; i >= int(n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) a.begin(), a.end()
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << " ";
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int Log2(ll x) {
  int k;
  for (k = 0; x > 0; ++k)
    x >>= 1;
  return k;
} // number of binary digits
const int INF = 1 << 30;
const ll INFll = 1ll << 62;
const ld EPS = 1e-10;
const ld PI = acos(-1.0);
const int MOD = int(1e9) + 7;

ll solve(ll a, ll b) {
  if (a == b)
    return 1;
  if (Log2(a) == Log2(b)) {
    a ^= (1ll << (Log2(a) - 1));
    b ^= (1ll << (Log2(b) - 1));
    return solve(a, b);
  }

  ll ans = 0;

  ll c = b;
  int d1 = Log2(b);
  c = b - (1ll << (d1 - 1));
  int d2 = Log2(c);
  c = (1ll << d2) - 1;
  c += (1ll << (d1 - 1));

  ans += c - a + 1;

  ll e = (1ll << (d1 - 1)) + a;
  ll f = (1ll << d1) - 1;
  if (c < e)
    ans += f - e + 1;
  else
    ans += f - c;

  return ans;
}

int main() {
  ll a, b;
  cin >> a >> b;
  cout << solve(a, b) << "\n";
  return 0;
}