Problem p00875 (C++) — buggy submission, verdict: Time Limit Exceeded

////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include "bits/stdc++.h"
using namespace std;

// -- loop macros -- //
#define REP(i, n) for (int i = 0; i < (n); i++)
#define RREP(i, n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i, s, n) for (int i = (int)(s); i < (n); i++)
#define RFOR(i, s, n) for (int i = (n)-1; i >= (s); i--)
#define FOREACH(i, container) for (auto &&i : container)
#define allof(c) c.begin(), c.end()
#define partof(c, i, n) c.begin() + (i), c.begin() + (i) + (n)

// -- functors -- //
#define PREDICATE(t, a, exp) [&](const t &a) -> bool { return exp; }
#define COMPARISON(t, a, b, exp)                                               \\
  [&](const t &a, const t &b) -> bool { return exp; }

#define PRED(a, exp) [&](const auto &a) -> bool { return exp; }
#define COMP(a, b, exp)                                                        \\
  [&](const auto &a, const auto &b) -> bool { return exp; }
#define CONV1(a, exp)                                                          \\
  [&](const auto &a) -> auto{ return exp; }
#define CONV2(a, b, exp)                                                       \\
  [&](const auto &a, const auto &b) -> auto{ return exp; }
#define CONV3(a, b, c, exp)                                                    \\
  [&](const auto &a, const auto &b, const auto &c) -> auto{ return exp; }

// -- typedefs -- //
#define EPS 1e-9

typedef unsigned int uint;
typedef long long llong;
typedef unsigned long long ullong;

// -- I/O Helper -- //
struct _Reader {
  _Reader(istream &cin) : cin(cin) {}
  istream &cin;
  template <class T> _Reader operator,(T &rhs) {
    cin >> rhs;
    return *this;
  }
};
struct _Writer {
  _Writer(ostream &cout) : cout(cout) {}
  ostream &cout;
  bool f{false};
  template <class T> _Writer operator,(const T &rhs) {
    cout << (f ? " " : "") << rhs;
    f = true;
    return *this;
  }
};
#define READ(t, ...)                                                           \\
  t __VA_ARGS__;                                                               \\
  (_Reader{cin}), __VA_ARGS__
#define WRITE(...)                                                             \\
  (_Writer{cout}), __VA_ARGS__;                                                \\
  cout << '\\n'
#define DEBUG(...)                                                             \\
  (_Writer{cerr}), __VA_ARGS__;                                                \\
  cerr << '\\n'

// -- vevector -- //
template <class T> struct vevector : public vector<vector<T>> {
  vevector(size_t n = 0, size_t m = 0, const T &initial = T())
      : vector<vector<T>>(n, vector<T>(m, initial)) {}
};
template <class T> struct vevevector : public vector<vevector<T>> {
  vevevector(size_t n = 0, size_t m = 0, size_t l = 0, const T &initial = T())
      : vector<vevector<T>>(n, vevector<T>(m, l, initial)) {}
};
template <class T> struct vevevevector : public vector<vevevector<T>> {
  vevevevector(size_t n = 0, size_t m = 0, size_t l = 0, size_t k = 0,
               const T &initial = T())
      : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) {}
};

namespace std {
template <class T1, class T2>
inline istream &operator>>(istream &in, pair<T1, T2> &p) {
  in >> p.first >> p.second;
  return in;
}
template <class T1, class T2>
inline ostream &operator<<(ostream &out, const pair<T1, T2> &p) {
  out << p.first << " " << p.second;
  return out;
}
} // namespace std

template <class T> T read() {
  T t;
  cin >> t;
  return t;
}
template <class T> vector<T> read(int n) {
  vector<T> v;
  REP(i, n) { v.push_back(read<T>()); }
  return v;
}
template <class T> vevector<T> read(int n, int m) {
  vevector<T> v;
  REP(i, n) v.push_back(read<T>(m));
  return v;
}
template <class T> vector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) {
  vevector<T> v;
  REP(i, n) v.push_back(readjag<T>());
  return v;
}

template <class T> struct iter_pair_t {
  T beg, end;
};
template <class T> iter_pair_t<T> iter_pair(T beg, T end) {
  return iter_pair_t<T>{beg, end};
}
template <class T> ostream &operator<<(ostream &out, iter_pair_t<T> v) {
  if (v.beg != v.end) {
    out << *v.beg++;
    while (v.beg != v.end) {
      out << " " << *v.beg++;
    }
  }
  return out;
}
template <class T1> ostream &operator<<(ostream &out, const vector<T1> &v) {
  return out << iter_pair(begin(v), end(v));
}

// -- etc -- //
template <class T> T infinity_value();
#define DEFINE_INFINITY_VALUE(T, val)                                          \\
  template <> constexpr T infinity_value<T>() { return (val); }
DEFINE_INFINITY_VALUE(int, 1 << 28);
DEFINE_INFINITY_VALUE(uint, 1u << 28);
DEFINE_INFINITY_VALUE(llong, 1ll << 60);
DEFINE_INFINITY_VALUE(ullong, 1ull << 60);
DEFINE_INFINITY_VALUE(double, HUGE_VAL);
DEFINE_INFINITY_VALUE(float, HUGE_VAL);
#define INF(T) infinity_value<T>()

inline int sign_of(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
template <class TInt> bool in_range(TInt val, TInt min, TInt max) {
  return val >= min && val < max;
}
template <> bool in_range<double>(double val, double min, double max) {
  return val - min > -EPS && val - max < EPS;
}
template <> bool in_range<float>(float val, float min, float max) {
  return val - min > -EPS && val - max < EPS;
}
template <class TInt> bool in_range2d(TInt x, TInt y, TInt w, TInt h) {
  return x >= 0 && x < w && y >= 0 && y < h;
}
vector<int> iotavn(int start, int count) {
  vector<int> r(count);
  iota(allof(r), start);
  return r;
}

// 文字列の分割
vector<string> split(const string &str, const string &s,
                     bool removeEmpty = false) {
  vector<string> ret;
  size_t p = 0, sl = s.size();
  while (true) {
    size_t q = str.find(s, p);
    if (q == str.npos)
      break;
    ret.push_back(str.substr(p, q - p));
    p = q + sl;
  }
  ret.push_back(str.substr(p));
  if (removeEmpty)
    ret.erase(remove(allof(ret), string()), ret.end());
  return ret;
}

//// start up ////
void solve();
int main() {
  //// for local debugging
  // freopen("input.txt", "r", stdin);
  // freopen("output.txt", "w", stdout);

  // auto classic_table = ctype<char>::classic_table();
  // vector<ctype<char>::mask> ctable(classic_table, classic_table +
  // ctype<char>::table_size); ctable[':'] |= ctype_base::space; // as delimitor
  // ctable[','] |= ctype_base::space; // as delimitor
  // cin.imbue(locale(cin.getloc(), new ctype<char>(ctable.data())));

  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cout << fixed;
  cout << setprecision(std::numeric_limits<double>::max_digits10);
  solve();

  return 0;
}

////////////////////
/// template end ///
////////////////////

// 文字列の置換
void inplaceReplace(string &target, const string &from, const string &to,
                    bool global = false) {
  string::size_type p = 0;
  do {
    string::size_type pos = target.find(from, p);
    if (pos == target.npos) {
      break;
    }
    target.replace(pos, from.length(), to);
    p = pos + to.length();
  } while (global);
}

void solve() {
  while (true) {
    READ(int, N);
    if (!N) {
      break;
    }
    auto subst = read<pair<string, string>>(N);
    READ(string, g, d);

    map<string, int> a;
    queue<pair<string, int>> q;
    q.push({g, 0});
    while (!q.empty()) {
      auto p = q.front();
      q.pop();
      // DEBUG(p.first);
      FOREACH(s, subst) {
        auto n = p.first;
        inplaceReplace(n, s.first, s.second, true);

        if (n.size() <= d.size() && !a.count(n)) {
          a[n] = p.second + 1;
          q.push({n, p.second + 1});
        }
        if (n == d) {
          break;
        }
      }
    }
    WRITE(a.count(d) ? a[d] : -1);
  }
}


Error: TLE

Fixed submission:

////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include "bits/stdc++.h"
using namespace std;

// -- loop macros -- //
#define REP(i, n) for (int i = 0; i < (n); i++)
#define RREP(i, n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i, s, n) for (int i = (int)(s); i < (n); i++)
#define RFOR(i, s, n) for (int i = (n)-1; i >= (s); i--)
#define FOREACH(i, container) for (auto &&i : container)
#define allof(c) c.begin(), c.end()
#define partof(c, i, n) c.begin() + (i), c.begin() + (i) + (n)

// -- functors -- //
#define PREDICATE(t, a, exp) [&](const t &a) -> bool { return exp; }
#define COMPARISON(t, a, b, exp)                                               \\
  [&](const t &a, const t &b) -> bool { return exp; }

#define PRED(a, exp) [&](const auto &a) -> bool { return exp; }
#define COMP(a, b, exp)                                                        \\
  [&](const auto &a, const auto &b) -> bool { return exp; }
#define CONV1(a, exp)                                                          \\
  [&](const auto &a) -> auto{ return exp; }
#define CONV2(a, b, exp)                                                       \\
  [&](const auto &a, const auto &b) -> auto{ return exp; }
#define CONV3(a, b, c, exp)                                                    \\
  [&](const auto &a, const auto &b, const auto &c) -> auto{ return exp; }

// -- typedefs -- //
#define EPS 1e-9

typedef unsigned int uint;
typedef long long llong;
typedef unsigned long long ullong;

// -- I/O Helper -- //
struct _Reader {
  _Reader(istream &cin) : cin(cin) {}
  istream &cin;
  template <class T> _Reader operator,(T &rhs) {
    cin >> rhs;
    return *this;
  }
};
struct _Writer {
  _Writer(ostream &cout) : cout(cout) {}
  ostream &cout;
  bool f{false};
  template <class T> _Writer operator,(const T &rhs) {
    cout << (f ? " " : "") << rhs;
    f = true;
    return *this;
  }
};
#define READ(t, ...)                                                           \\
  t __VA_ARGS__;                                                               \\
  (_Reader{cin}), __VA_ARGS__
#define WRITE(...)                                                             \\
  (_Writer{cout}), __VA_ARGS__;                                                \\
  cout << '\\n'
#define DEBUG(...)                                                             \\
  (_Writer{cerr}), __VA_ARGS__;                                                \\
  cerr << '\\n'

// -- vevector -- //
template <class T> struct vevector : public vector<vector<T>> {
  vevector(size_t n = 0, size_t m = 0, const T &initial = T())
      : vector<vector<T>>(n, vector<T>(m, initial)) {}
};
template <class T> struct vevevector : public vector<vevector<T>> {
  vevevector(size_t n = 0, size_t m = 0, size_t l = 0, const T &initial = T())
      : vector<vevector<T>>(n, vevector<T>(m, l, initial)) {}
};
template <class T> struct vevevevector : public vector<vevevector<T>> {
  vevevevector(size_t n = 0, size_t m = 0, size_t l = 0, size_t k = 0,
               const T &initial = T())
      : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) {}
};

namespace std {
template <class T1, class T2>
inline istream &operator>>(istream &in, pair<T1, T2> &p) {
  in >> p.first >> p.second;
  return in;
}
template <class T1, class T2>
inline ostream &operator<<(ostream &out, const pair<T1, T2> &p) {
  out << p.first << " " << p.second;
  return out;
}
} // namespace std

template <class T> T read() {
  T t;
  cin >> t;
  return t;
}
template <class T> vector<T> read(int n) {
  vector<T> v;
  REP(i, n) { v.push_back(read<T>()); }
  return v;
}
template <class T> vevector<T> read(int n, int m) {
  vevector<T> v;
  REP(i, n) v.push_back(read<T>(m));
  return v;
}
template <class T> vector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) {
  vevector<T> v;
  REP(i, n) v.push_back(readjag<T>());
  return v;
}

template <class T> struct iter_pair_t {
  T beg, end;
};
template <class T> iter_pair_t<T> iter_pair(T beg, T end) {
  return iter_pair_t<T>{beg, end};
}
template <class T> ostream &operator<<(ostream &out, iter_pair_t<T> v) {
  if (v.beg != v.end) {
    out << *v.beg++;
    while (v.beg != v.end) {
      out << " " << *v.beg++;
    }
  }
  return out;
}
template <class T1> ostream &operator<<(ostream &out, const vector<T1> &v) {
  return out << iter_pair(begin(v), end(v));
}

// -- etc -- //
template <class T> T infinity_value();
#define DEFINE_INFINITY_VALUE(T, val)                                          \\
  template <> constexpr T infinity_value<T>() { return (val); }
DEFINE_INFINITY_VALUE(int, 1 << 28);
DEFINE_INFINITY_VALUE(uint, 1u << 28);
DEFINE_INFINITY_VALUE(llong, 1ll << 60);
DEFINE_INFINITY_VALUE(ullong, 1ull << 60);
DEFINE_INFINITY_VALUE(double, HUGE_VAL);
DEFINE_INFINITY_VALUE(float, HUGE_VAL);
#define INF(T) infinity_value<T>()

inline int sign_of(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
template <class TInt> bool in_range(TInt val, TInt min, TInt max) {
  return val >= min && val < max;
}
template <> bool in_range<double>(double val, double min, double max) {
  return val - min > -EPS && val - max < EPS;
}
template <> bool in_range<float>(float val, float min, float max) {
  return val - min > -EPS && val - max < EPS;
}
template <class TInt> bool in_range2d(TInt x, TInt y, TInt w, TInt h) {
  return x >= 0 && x < w && y >= 0 && y < h;
}
vector<int> iotavn(int start, int count) {
  vector<int> r(count);
  iota(allof(r), start);
  return r;
}

// 文字列の分割
vector<string> split(const string &str, const string &s,
                     bool removeEmpty = false) {
  vector<string> ret;
  size_t p = 0, sl = s.size();
  while (true) {
    size_t q = str.find(s, p);
    if (q == str.npos)
      break;
    ret.push_back(str.substr(p, q - p));
    p = q + sl;
  }
  ret.push_back(str.substr(p));
  if (removeEmpty)
    ret.erase(remove(allof(ret), string()), ret.end());
  return ret;
}

//// start up ////
void solve();
int main() {
  //// for local debugging
  // freopen("input.txt", "r", stdin);
  // freopen("output.txt", "w", stdout);

  // auto classic_table = ctype<char>::classic_table();
  // vector<ctype<char>::mask> ctable(classic_table, classic_table +
  // ctype<char>::table_size); ctable[':'] |= ctype_base::space; // as delimitor
  // ctable[','] |= ctype_base::space; // as delimitor
  // cin.imbue(locale(cin.getloc(), new ctype<char>(ctable.data())));

  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cout << fixed;
  cout << setprecision(std::numeric_limits<double>::max_digits10);
  solve();

  return 0;
}

////////////////////
/// template end ///
////////////////////

// 文字列の置換
void inplaceReplace(string &target, const string &from, const string &to,
                    bool global = false) {
  string::size_type p = 0;
  do {
    string::size_type pos = target.find(from, p);
    if (pos == target.npos) {
      break;
    }
    target.replace(pos, from.length(), to);
    p = pos + to.length();
  } while (global);
}

void solve() {
  while (true) {
    READ(int, N);
    auto subst = read<pair<string, string>>(N);
    READ(string, g, d);

    map<string, int> a;
    queue<pair<string, int>> q;
    q.push({g, 0});
    while (!q.empty()) {
      auto p = q.front();
      q.pop();
      // DEBUG(p.first);
      FOREACH(s, subst) {
        auto n = p.first;
        inplaceReplace(n, s.first, s.second, true);

        if (n.size() <= d.size() && !a.count(n)) {
          a[n] = p.second + 1;
          q.push({n, p.second + 1});
        }
        if (n == d) {
          break;
        }
      }
    }
    WRITE(a.count(d) ? a[d] : -1);
  }
}