Problem p02964 (C++)

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

using namespace std;

#define int long long
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
#define rAll(a) (a).rbegin(), (a).rend()
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(...)                                                              \
  ll __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 pair<ll, ll> PL;
typedef vector<PL> VPL;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef vector<double> VD;

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 dx[] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
#define PI 3.141592653589793238

ll N, K;
VL A(200000);

VVL doubling(ll N, const VL &A) {
  VL used(200010, -1);
  VVL ret(61, VL(N));
  REP(k, 2) REP(i, N) {
    if (used[A[i]] != -1) {
      ret[0][used[A[i]] % N] = k * N + i - used[A[i]] + 1;
    }
    used[A[i]] = k * N + i;
  }
  FOR(k, 1, 60) REP(i, N) {
    ret[k][i] = ret[k - 1][i] + ret[k - 1][(i + ret[k - 1][i]) % N];
  }
  return ret;
}

signed main() {
  cin >> N >> K;
  REP(i, N) cin >> A[i];
  VVL dbl = doubling(N, A);
  ll now = 0, sum = 0, C = N * K;
  while (1) {
    ll num = 0;
    REP(k, 60) {
      if (dbl[k][now] + sum >= C) {
        num = k - 1;
        break;
      }
    }
    if (num == -1)
      break;
    sum += dbl[num][now];
    now = sum % N;
  }
  vector<bool> exist(N, false);
  stack<ll> st;
  while (sum < C) {
    if (!exist[A[now]]) {
      st.emplace(A[now]);
      exist[A[now]] = true;
    } else {
      while (exist[A[now]]) {
        exist[st.top()] = false;
        st.pop();
      }
    }
    now++;
    if (now == N)
      break;
  }
  VL ans;
  while (st.size()) {
    ans.emplace_back(st.top());
    st.pop();
  }
  REPR(i, ans.size() - 1) cout << ans[i] << (i ? " " : "\n");
}

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

using namespace std;

#define int long long
#define FOR(i, a, b) for (ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for (ll i = (a); i > (b); --i)
#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOREACH(x, a) for (auto &(x) : (a))
#define VECCIN(x)                                                              \
  for (auto &youso_ : (x))                                                     \
  cin >> youso_
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
#define rAll(a) (a).rbegin(), (a).rend()
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(...)                                                              \
  ll __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 pair<ll, ll> PL;
typedef vector<PL> VPL;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef vector<double> VD;

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 dx[] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
#define PI 3.141592653589793238

ll N, K;
VL A(200000);

VVL doubling(ll N, const VL &A) {
  VL used(200010, -1);
  VVL ret(61, VL(N));
  REP(k, 2) REP(i, N) {
    if (used[A[i]] != -1) {
      ret[0][used[A[i]] % N] = k * N + i - used[A[i]] + 1;
    }
    used[A[i]] = k * N + i;
  }
  FOR(k, 1, 60) REP(i, N) {
    ret[k][i] = ret[k - 1][i] + ret[k - 1][(i + ret[k - 1][i]) % N];
  }
  return ret;
}

signed main() {
  cin >> N >> K;
  REP(i, N) cin >> A[i];
  VVL dbl = doubling(N, A);
  ll now = 0, sum = 0, C = N * K;
  while (1) {
    ll num = 0;
    REP(k, 60) {
      if (dbl[k][now] + sum >= C) {
        num = k - 1;
        break;
      }
    }
    if (num == -1)
      break;
    sum += dbl[num][now];
    now = sum % N;
  }
  vector<bool> exist(200010, false);
  stack<ll> st;
  while (sum < C) {
    if (!exist[A[now]]) {
      st.emplace(A[now]);
      exist[A[now]] = true;
    } else {
      while (exist[A[now]]) {
        exist[st.top()] = false;
        st.pop();
      }
    }
    now++;
    if (now == N)
      break;
  }
  VL ans;
  while (st.size()) {
    ans.emplace_back(st.top());
    st.pop();
  }
  REPR(i, ans.size() - 1) cout << ans[i] << (i ? " " : "\n");
}