Problem p02550 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
// #define LOCAL // 提出時はコメントアウト
#define DEBUG_

typedef long long ll;
const double EPS = 1e-9;
const ll INF = ((1LL << 62) - (1LL << 31));
typedef vector<ll> vecl;
typedef pair<ll, ll> pairl;
template <typename T, typename U> using mapv = map<T, vector<U>>;

#define ALL(v) v.begin(), v.end()
#define REP(i, x, n) for (int i = x; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define contains(S, x) find(ALL(S), x) != S.end()
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> vector<vector<T>> genarr(ll n, ll m, T init) {
  return vector<vector<T>>(n, vector<T>(m, init));
}

///// DEBUG
#define DUMPOUT cerr
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  }
  os << "}";
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}
#ifndef LOCAL
#undef DEBUG_
#endif
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

//////////

int main() {
#ifdef LOCAL
  ifstream in("../../Atcoder/input.txt");
  cin.rdbuf(in.rdbuf());
#endif

  ll N, X, M;
  cin >> N >> X >> M;

  unordered_set<ll> seen;
  vecl memo;
  ll x = X;

  seen.insert(X);
  memo.push_back(X);

  ll dup_i = 0;
  ll dup = 0;

  ll ans = X;
  if (N == 1) {
    cout << ans << endl;
    return 0;
  }
  rep(i, N) {
    x = (x % M) * (x % M) % M;
    if (seen.count(x) > 0) {
      dup_i = memo.size();
      dup = x;
      break;
    }
    memo.push_back(x);
    seen.insert(x);
    ans += x;
    if (i == N - 2) { // 重複なければ、そのまま答え
      cout << ans << endl;
      dump("normal");
      return 0;
    }
  }
  dump(memo);
  dump(dup_i, dup, ans);

  ll window = 0;
  ll dup_origin = 0;
  // ll window_sum = dup;
  vecl window_sum(memo.size() + 10, 0);
  // window_sum[1] = dup;
  ll window_i = 0;
  bool found = false;

  ans = 0;
  rep(i, memo.size()) {
    if (found) {
      // window_sum += memo[i];
      window_sum[window_i + 1] += memo[i] + window_sum[window_i];
      window_i++;
      continue;
    }
    if (memo[i] == dup) {
      dup_origin = i;
      window = dup_i - i;
      found = true;
      window_sum[window_i + 1] += memo[i] + window_sum[window_i];
      window_i++;
      continue;
    }
    ans += memo[i]; // window以外は先に足す
  }

  dump(dup_origin, ans);

  ll r = N - 1 - (dup_origin - 1);
  ll ref_size = floor(r / window);
  ll over = r % window;

  ans += window_sum[window_i] * ref_size;
  dump(r, window, ref_size, ans);

  // ll over_count = 0;
  // REP(i,dup_origin,memo.size()) {
  //     if (over_count == over) break;
  //     ans += memo[i];
  //     over_count++;
  // }

  ans += window_sum[over];

  cout << ans << endl;

  return 0;
}


Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
// #define LOCAL // 提出時はコメントアウト
#define DEBUG_

typedef long long ll;
const double EPS = 1e-9;
const ll INF = ((1LL << 62) - (1LL << 31));
typedef vector<ll> vecl;
typedef pair<ll, ll> pairl;
template <typename T, typename U> using mapv = map<T, vector<U>>;

#define ALL(v) v.begin(), v.end()
#define REP(i, x, n) for (int i = x; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define contains(S, x) find(ALL(S), x) != S.end()
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> vector<vector<T>> genarr(ll n, ll m, T init) {
  return vector<vector<T>>(n, vector<T>(m, init));
}

///// DEBUG
#define DUMPOUT cerr
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  }
  os << "}";
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}
#ifndef LOCAL
#undef DEBUG_
#endif
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

//////////

int main() {
#ifdef LOCAL
  ifstream in("../../Atcoder/input.txt");
  cin.rdbuf(in.rdbuf());
#endif

  ll N, X, M;
  cin >> N >> X >> M;

  unordered_set<ll> seen;
  vecl memo;
  ll x = X;

  seen.insert(X);
  memo.push_back(X);

  ll dup_i = 0;
  ll dup = 0;

  ll ans = X;
  if (N == 1) {
    cout << ans << endl;
    return 0;
  }
  rep(i, N) {
    x = (x % M) * (x % M) % M;
    if (find(ALL(seen), x) != seen.end()) {
      dup_i = memo.size();
      dup = x;
      break;
    }
    memo.push_back(x);
    seen.insert(x);
    ans += x;
    if (i == N - 2) { // 重複なければ、そのまま答え
      cout << ans << endl;
      dump("normal");
      return 0;
    }
  }
  return 1;
}