Problem p02962 (C++)

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

using namespace std;

#define int long long
// #define double long double
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORR(i, a, b) for (int i = (a); i > (b); --i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt(x) __builtin_popcount(x)
#define lbit(x) __builtin_ffsll(x)
#define rbit(x) __builtin_clzll(x)
#define SZ(x) ((long long)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
#define rAll(a) (a).rbegin(), (a).rend()
#define cinfast() cin.tie(0), ios::sync_with_stdio(false)
#define PERM(c)                                                                \
  sort(All(c));                                                                \
  for (bool cp = true; cp; cp = next_permutation(All(c)))
#define MKORDER(n)                                                             \
  vector<int> od(n);                                                           \
  iota(All(od), 0LL);

template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CCIN(...)                                                              \
  char __VA_ARGS__;                                                            \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  long long __VA_ARGS__;                                                       \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
  {                                                                            \
    FOREACH(x, v) { cout << x << " "; }                                        \
    cout << "\n";                                                              \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<ll, ll> PL;
typedef vector<PL> VPL;
typedef vector<bool> VB;
typedef vector<double> VD;
typedef vector<string> VS;

const int INF = 1e9;
const int MOD = 1e9 + 7;
// const int MOD = 998244353;
const ll LINF = 1e18;
const double PI = atan(1.0) * 4.0;
const ll dw[] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dh[] = {0, 1, 1, 1, 0, -1, -1, -1};
#define PI 3.141592653589793238

VL Zalgo(const string &S) {
  int N = (int)S.size();
  VL res(N);
  res[0] = N;
  int i = 1, j = 0;
  while (i < N) {
    while (i + j < N && S[j] == S[i + j])
      ++j;
    res[i] = j;
    if (j == 0) {
      ++i;
      continue;
    }
    int k = 1;
    while (i + k < N && k + res[k] < j)
      res[i + k] = res[k], ++k;
    i += k, j -= k;
  }
  return res;
}

VVL G;
VB used, nused;
set<ll> st;
VL hist;
bool finished[1000];
ll start = -1;

void findroop(int v) {
  used[v] = true;
  hist.emplace_back(v);
  FOREACH(to, G[v]) {
    if (finished[to])
      continue;
    if (used[to]) {
      start = to;
      return;
    }
    findroop(to);
    if (start != -1)
      return;
  }
  hist.pop_back();
  finished[v] = true;
}

bool dfs(ll now) {
  st.emplace(now);
  used[now] = true;
  bool res = true;
  FOREACH(to, G[now]) {
    if (res == false)
      break;
    if (st.find(to) != st.end())
      return false;
    res &= dfs(to);
  }
  return res;
}

ll dfs2(ll now, ll par) {
  used[now] = true;
  ll res = 0;
  FOREACH(to, G[now]) {
    if (to == par || used[to])
      continue;
    res = max(res, dfs2(to, now) + 1);
  }
  return res;
}

signed main() {
  SCIN(S, T);
  string tmp = S;
  while (tmp.length() < T.length()) {
    tmp += S;
  }
  VL z = Zalgo(T + "$" + tmp + tmp);
  ll N = tmp.length();
  G.resize(N);
  REP(i, N) {
    if (z[T.length() + 1 + i] == T.length()) {
      G[i].emplace_back((i + T.length()) % N);
    }
  }
  used.assign(N, false);
  ll ans = 0;
  REP(i, N) {
    if (used[i])
      continue;
    findroop(i);
    if (start != -1)
      eputs(-1);
  }
  used.assign(N, false);
  REP(i, N) {
    if (used[i])
      continue;
    st.clear();
    dfs(i);
    ans = max(ans, (ll)st.size() - 1);
  }
  cout << ans << "\n";
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;

#define int long long
// #define double long double
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORR(i, a, b) for (int i = (a); i > (b); --i)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt(x) __builtin_popcount(x)
#define lbit(x) __builtin_ffsll(x)
#define rbit(x) __builtin_clzll(x)
#define SZ(x) ((long long)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
#define rAll(a) (a).rbegin(), (a).rend()
#define cinfast() cin.tie(0), ios::sync_with_stdio(false)
#define PERM(c)                                                                \
  sort(All(c));                                                                \
  for (bool cp = true; cp; cp = next_permutation(All(c)))
#define MKORDER(n)                                                             \
  vector<int> od(n);                                                           \
  iota(All(od), 0LL);

template <typename T = long long> inline T IN() {
  T x;
  cin >> x;
  return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&...tail) {
  cin >> head;
  CIN(move(tail)...);
}
#define CCIN(...)                                                              \
  char __VA_ARGS__;                                                            \
  CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
  double __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
  long long __VA_ARGS__;                                                       \
  CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
  string __VA_ARGS__;                                                          \
  CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
  {                                                                            \
    FOREACH(x, v) { cout << x << " "; }                                        \
    cout << "\n";                                                              \
  }
template <typename T = string> inline void eputs(T s) {
  cout << s << "\n";
  exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<ll, ll> PL;
typedef vector<PL> VPL;
typedef vector<bool> VB;
typedef vector<double> VD;
typedef vector<string> VS;

const int INF = 1e9;
const int MOD = 1e9 + 7;
// const int MOD = 998244353;
const ll LINF = 1e18;
const double PI = atan(1.0) * 4.0;
const ll dw[] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dh[] = {0, 1, 1, 1, 0, -1, -1, -1};
#define PI 3.141592653589793238

VL Zalgo(const string &S) {
  int N = (int)S.size();
  VL res(N);
  res[0] = N;
  int i = 1, j = 0;
  while (i < N) {
    while (i + j < N && S[j] == S[i + j])
      ++j;
    res[i] = j;
    if (j == 0) {
      ++i;
      continue;
    }
    int k = 1;
    while (i + k < N && k + res[k] < j)
      res[i + k] = res[k], ++k;
    i += k, j -= k;
  }
  return res;
}

VVL G;
VB used, nused;
set<ll> st;
VL hist;
bool finished[1000100];
ll start = -1;

void findroop(int v) {
  used[v] = true;
  hist.emplace_back(v);
  FOREACH(to, G[v]) {
    if (finished[to])
      continue;
    if (used[to]) {
      start = to;
      return;
    }
    findroop(to);
    if (start != -1)
      return;
  }
  hist.pop_back();
  finished[v] = true;
}

bool dfs(ll now) {
  st.emplace(now);
  used[now] = true;
  bool res = true;
  FOREACH(to, G[now]) {
    if (res == false)
      break;
    if (st.find(to) != st.end())
      return false;
    res &= dfs(to);
  }
  return res;
}

ll dfs2(ll now, ll par) {
  used[now] = true;
  ll res = 0;
  FOREACH(to, G[now]) {
    if (to == par || used[to])
      continue;
    res = max(res, dfs2(to, now) + 1);
  }
  return res;
}

signed main() {
  SCIN(S, T);
  string tmp = S;
  while (tmp.length() < T.length()) {
    tmp += S;
  }
  VL z = Zalgo(T + "$" + tmp + tmp);
  ll N = tmp.length();
  G.resize(N);
  REP(i, N) {
    if (z[T.length() + 1 + i] == T.length()) {
      G[i].emplace_back((i + T.length()) % N);
    }
  }
  used.assign(N, false);
  ll ans = 0;
  REP(i, N) {
    if (used[i])
      continue;
    findroop(i);
    if (start != -1)
      eputs(-1);
  }
  used.assign(N, false);
  REP(i, N) {
    if (used[i])
      continue;
    st.clear();
    dfs(i);
    ans = max(ans, (ll)st.size() - 1);
  }
  cout << ans << "\n";
}