Problem p03680 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#if __has_include(<boost/multiprecision/cpp_int.hpp>)
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>
using bll = boost::multiprecision::cpp_int;
using bdouble =
    boost::multiprecision::number<boost::multiprecision::cpp_dec_float<100>>;
using namespace boost::multiprecision;
#endif
#if __has_include(<boost/stacktrace.hpp>)
#define BOOST_STACKTRACE_USE_ADDR2LINE
#define BOOST_STACKTRACE_ADDR2LINE_LOCATION                                    \
  / usr / local / opt / binutils / bin / addr2line
#define _GNU_SOURCE 1
#include <boost/stacktrace.hpp>
#endif
#ifdef LOCAL_TEST
namespace std {
template <typename T> class dvector : public std::vector<T> {
public:
  dvector() : std::vector<T>() {}
  explicit dvector(size_t n, const T &value = T()) : std::vector<T>(n, value) {}
  dvector(const std::vector<T> &v) : std::vector<T>(v) {}
  dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
  dvector(const std::string::iterator first, const std::string::iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::iterator first,
          const typename std::vector<T>::iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::reverse_iterator first,
          const typename std::vector<T>::reverse_iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::const_iterator first,
          const typename std::vector<T>::const_iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::const_reverse_iterator first,
          const typename std::vector<T>::const_reverse_iterator last)
      : std::vector<T>(first, last) {}
  T &operator[](size_t n) {
    try {
      return this->at(n);
    } catch (const std::exception &e) {
      std::cerr << boost::stacktrace::stacktrace() << '\n';
      return this->at(n);
    }
  }
  const T &operator[](size_t n) const {
    try {
      return this->at(n);
    } catch (const std::exception &e) {
      std::cerr << boost::stacktrace::stacktrace() << '\n';
      return this->at(n);
    }
  }
};
} // namespace std
class dbool {
private:
  bool boolvalue;

public:
  dbool() : boolvalue(false) {}
  dbool(bool b) : boolvalue(b) {}
  operator bool &() { return boolvalue; }
  operator const bool &() const { return boolvalue; }
};
#define vector dvector
#define bool dbool
#endif
#ifdef LOCAL_DEV
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::vector<T> &v) {
  for (size_t i = 0; i < v.size(); ++i) {
    s << v[i];
    if (i < v.size() - 1)
      s << "\t";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s,
                         const std::vector<std::vector<T>> &vv) {
  s << "\\\n";
  for (size_t i = 0; i < vv.size(); ++i) {
    s << vv[i] << "\n";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::deque<T> &v) {
  for (size_t i = 0; i < v.size(); ++i) {
    s << v[i];
    if (i < v.size() - 1)
      s << "\t";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::set<T> &se) {
  s << "{ ";
  for (auto itr = se.begin(); itr != se.end(); ++itr) {
    s << (*itr) << "\t";
  }
  s << "}";
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::multiset<T> &se) {
  s << "{ ";
  for (auto itr = se.begin(); itr != se.end(); ++itr) {
    s << (*itr) << "\t";
  }
  s << "}";
  return s;
}
template <typename T, size_t N>
std::ostream &operator<<(std::ostream &s, const std::array<T, N> &a) {
  s << "{ ";
  for (size_t i = 0; i < N; ++i) {
    s << a[i] << "\t";
  }
  s << "}";
  return s;
}
template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &s, const std::map<T1, T2> &m) {
  s << "{\n";
  for (auto itr = m.begin(); itr != m.end(); ++itr) {
    s << "\t" << (*itr).first << " : " << (*itr).second << "\n";
  }
  s << "}";
  return s;
}
template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &s, const std::pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}
class SIGFPE_exception : std::exception {};
class SIGSEGV_exception : std::exception {};
void catch_SIGFPE([[maybe_unused]] int e) {
  std::cerr << boost::stacktrace::stacktrace() << '\n';
  throw SIGFPE_exception();
}
void catch_SIGSEGV([[maybe_unused]] int e) {
  std::cerr << boost::stacktrace::stacktrace() << '\n';
  throw SIGSEGV_exception();
}
signed convertedmain();
signed main() {
  signal(SIGFPE, catch_SIGFPE);
  signal(SIGSEGV, catch_SIGSEGV);
  return convertedmain();
}
#define main() convertedmain()
void debug_impl() { std::cerr << '\n'; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) {
  std::cerr << " " << head << (sizeof...(tail) ? "," : "");
  debug_impl(tail...);
}
#define debug(...)                                                             \
  do {                                                                         \
    std::cerr << "(" << #__VA_ARGS__ << ") =";                                 \
    debug_impl(__VA_ARGS__);                                                   \
  } while (false)
#else
#define debug(...)                                                             \
  do {                                                                         \
  } while (false)
#endif
// #define int long long
using ll = long long;
// constexpr int INF = (ll)1e9 + 7;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18; //(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr ll dx[4] = {1, 0, -1, 0};
constexpr ll dy[4] = {0, 1, 0, -1};
constexpr ll dx8[8] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr ll dy8[8] = {0, 1, 0, -1, 1, -1, 1, -1};
#define rep(i, n) for (ll i = 0, i##_length = (n); i < i##_length; ++i)
#define repeq(i, n) for (ll i = 1, i##_length = (n); i <= i##_length; ++i)
#define rrep(i, n) for (ll i = (n)-1; i >= 0; --i)
#define rrepeq(i, n) for (ll i = (n); i >= 1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
void p() { std::cout << '\n'; }
template <typename Head, typename... Tail> void p(Head head, Tail... tail) {
  std::cout << head << (sizeof...(tail) ? " " : "");
  p(tail...);
}
template <typename T> inline void pv(std::vector<T> &v) {
  for (ll i = 0, N = v.size(); i < N; i++)
    std::cout << v[i] << " \n"[i == N - 1];
}
template <typename T> inline bool chmax(T &a, T b) {
  return a < b && (a = b, true);
}
template <typename T> inline bool chmin(T &a, T b) {
  return a > b && (a = b, true);
}
template <typename T> inline void uniq(std::vector<T> &v) {
  v.erase(std::unique(v.begin(), v.end()), v.end());
}

/*-----8<-----template-----8<-----*/

/*-----8<-----library-----8<-----*/

void solve() {
  ll N;
  cin >> N;
  vector<ll> a(N);
  rep(i, N) {
    cin >> a[i];
    a[i]--;
  }

  ll x = 0;
  ll ans = 0;
  vector<bool> seen(N, false);

  while (1) {
    if (x == 1) {
      p(ans);
      return;
    }
    if (seen[x]) {
      p(-1);
      return;
    }
    seen[0] = true;
    x = a[x];
    ans++;
  }
}

signed main() {
  solve();
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#if __has_include(<boost/multiprecision/cpp_int.hpp>)
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>
using bll = boost::multiprecision::cpp_int;
using bdouble =
    boost::multiprecision::number<boost::multiprecision::cpp_dec_float<100>>;
using namespace boost::multiprecision;
#endif
#if __has_include(<boost/stacktrace.hpp>)
#define BOOST_STACKTRACE_USE_ADDR2LINE
#define BOOST_STACKTRACE_ADDR2LINE_LOCATION                                    \
  / usr / local / opt / binutils / bin / addr2line
#define _GNU_SOURCE 1
#include <boost/stacktrace.hpp>
#endif
#ifdef LOCAL_TEST
namespace std {
template <typename T> class dvector : public std::vector<T> {
public:
  dvector() : std::vector<T>() {}
  explicit dvector(size_t n, const T &value = T()) : std::vector<T>(n, value) {}
  dvector(const std::vector<T> &v) : std::vector<T>(v) {}
  dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
  dvector(const std::string::iterator first, const std::string::iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::iterator first,
          const typename std::vector<T>::iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::reverse_iterator first,
          const typename std::vector<T>::reverse_iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::const_iterator first,
          const typename std::vector<T>::const_iterator last)
      : std::vector<T>(first, last) {}
  dvector(const typename std::vector<T>::const_reverse_iterator first,
          const typename std::vector<T>::const_reverse_iterator last)
      : std::vector<T>(first, last) {}
  T &operator[](size_t n) {
    try {
      return this->at(n);
    } catch (const std::exception &e) {
      std::cerr << boost::stacktrace::stacktrace() << '\n';
      return this->at(n);
    }
  }
  const T &operator[](size_t n) const {
    try {
      return this->at(n);
    } catch (const std::exception &e) {
      std::cerr << boost::stacktrace::stacktrace() << '\n';
      return this->at(n);
    }
  }
};
} // namespace std
class dbool {
private:
  bool boolvalue;

public:
  dbool() : boolvalue(false) {}
  dbool(bool b) : boolvalue(b) {}
  operator bool &() { return boolvalue; }
  operator const bool &() const { return boolvalue; }
};
#define vector dvector
#define bool dbool
#endif
#ifdef LOCAL_DEV
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::vector<T> &v) {
  for (size_t i = 0; i < v.size(); ++i) {
    s << v[i];
    if (i < v.size() - 1)
      s << "\t";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s,
                         const std::vector<std::vector<T>> &vv) {
  s << "\\\n";
  for (size_t i = 0; i < vv.size(); ++i) {
    s << vv[i] << "\n";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::deque<T> &v) {
  for (size_t i = 0; i < v.size(); ++i) {
    s << v[i];
    if (i < v.size() - 1)
      s << "\t";
  }
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::set<T> &se) {
  s << "{ ";
  for (auto itr = se.begin(); itr != se.end(); ++itr) {
    s << (*itr) << "\t";
  }
  s << "}";
  return s;
}
template <typename T>
std::ostream &operator<<(std::ostream &s, const std::multiset<T> &se) {
  s << "{ ";
  for (auto itr = se.begin(); itr != se.end(); ++itr) {
    s << (*itr) << "\t";
  }
  s << "}";
  return s;
}
template <typename T, size_t N>
std::ostream &operator<<(std::ostream &s, const std::array<T, N> &a) {
  s << "{ ";
  for (size_t i = 0; i < N; ++i) {
    s << a[i] << "\t";
  }
  s << "}";
  return s;
}
template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &s, const std::map<T1, T2> &m) {
  s << "{\n";
  for (auto itr = m.begin(); itr != m.end(); ++itr) {
    s << "\t" << (*itr).first << " : " << (*itr).second << "\n";
  }
  s << "}";
  return s;
}
template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &s, const std::pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}
class SIGFPE_exception : std::exception {};
class SIGSEGV_exception : std::exception {};
void catch_SIGFPE([[maybe_unused]] int e) {
  std::cerr << boost::stacktrace::stacktrace() << '\n';
  throw SIGFPE_exception();
}
void catch_SIGSEGV([[maybe_unused]] int e) {
  std::cerr << boost::stacktrace::stacktrace() << '\n';
  throw SIGSEGV_exception();
}
signed convertedmain();
signed main() {
  signal(SIGFPE, catch_SIGFPE);
  signal(SIGSEGV, catch_SIGSEGV);
  return convertedmain();
}
#define main() convertedmain()
void debug_impl() { std::cerr << '\n'; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) {
  std::cerr << " " << head << (sizeof...(tail) ? "," : "");
  debug_impl(tail...);
}
#define debug(...)                                                             \
  do {                                                                         \
    std::cerr << "(" << #__VA_ARGS__ << ") =";                                 \
    debug_impl(__VA_ARGS__);                                                   \
  } while (false)
#else
#define debug(...)                                                             \
  do {                                                                         \
  } while (false)
#endif
// #define int long long
using ll = long long;
// constexpr int INF = (ll)1e9 + 7;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18; //(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr ll dx[4] = {1, 0, -1, 0};
constexpr ll dy[4] = {0, 1, 0, -1};
constexpr ll dx8[8] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr ll dy8[8] = {0, 1, 0, -1, 1, -1, 1, -1};
#define rep(i, n) for (ll i = 0, i##_length = (n); i < i##_length; ++i)
#define repeq(i, n) for (ll i = 1, i##_length = (n); i <= i##_length; ++i)
#define rrep(i, n) for (ll i = (n)-1; i >= 0; --i)
#define rrepeq(i, n) for (ll i = (n); i >= 1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
void p() { std::cout << '\n'; }
template <typename Head, typename... Tail> void p(Head head, Tail... tail) {
  std::cout << head << (sizeof...(tail) ? " " : "");
  p(tail...);
}
template <typename T> inline void pv(std::vector<T> &v) {
  for (ll i = 0, N = v.size(); i < N; i++)
    std::cout << v[i] << " \n"[i == N - 1];
}
template <typename T> inline bool chmax(T &a, T b) {
  return a < b && (a = b, true);
}
template <typename T> inline bool chmin(T &a, T b) {
  return a > b && (a = b, true);
}
template <typename T> inline void uniq(std::vector<T> &v) {
  v.erase(std::unique(v.begin(), v.end()), v.end());
}

/*-----8<-----template-----8<-----*/

/*-----8<-----library-----8<-----*/

void solve() {
  ll N;
  cin >> N;
  vector<ll> a(N);
  rep(i, N) {
    cin >> a[i];
    a[i]--;
  }

  ll x = 0;
  ll ans = 0;
  vector<bool> seen(N, false);

  while (1) {
    if (x == 1) {
      p(ans);
      return;
    }
    if (seen[x]) {
      p(-1);
      return;
    }
    seen[x] = true;
    x = a[x];
    ans++;
  }
}

signed main() {
  solve();
  return 0;
}