Problem p02991 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <stdio.h>

using namespace std;
#define inputInt(a)                                                            \
  int a;                                                                       \
  cin >> a;
#define inputInt2(a, b)                                                        \
  int a;                                                                       \
  int b;                                                                       \
  cin >> a >> b;
#define inputInt3(a, b, c)                                                     \
  int a;                                                                       \
  int b;                                                                       \
  int c;                                                                       \
  cin >> a >> b >> c;
#define inputLong(a)                                                           \
  long a;                                                                      \
  cin >> a;
#define inputIntArray(a, N)                                                    \
  int a[N];                                                                    \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i];                                                               \
  }
#define inputLongArray(a, N)                                                   \
  long a[N];                                                                   \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i];                                                               \
  }
#define inputIntArray2(a, b, N)                                                \
  int a[N];                                                                    \
  int b[N];                                                                    \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i] >> b[i];                                                       \
  }
#define output(answer) cout << answer << endl;
#define fN(i, N) for (int i = 0; i < N; i++)
#define fSE(i, s, e) for (int i = s; i <= e; i++)
#define ll long long
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define FOR(i, N) for (int i = 0; i < N; i++)
#define cinv(v, N)                                                             \
  vector<int> v(N);                                                            \
  for (int i = 0; i < N; i++) {                                                \
    cin >> v[i];                                                               \
  }
#define mt make_tuple
#define vll vector<long long int>
#define vvll vector<vector<long long int>>
#define all(v) (v).begin(), (v).end()
#define show(v)                                                                \
  FOR(i, v.size()) { cout << v[i] << " "; }                                    \
  cout << endl;
#define showshow(v)                                                            \
  FOR(i, v.size()) {                                                           \
    FOR(j, v[i].size()) { cout << v[i][j] << " "; }                            \
    cout << endl;                                                              \
  }
const ll MOD = 1e9 + 7;
const ll MOD2 = 998244353;

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;
}

// Combination計算 //ComInitしないと何もできません。
const int LIMIT = 1e6; // 1e6→50ms,1e7→500ms,1e8→5000ms程度。
// const ll MOD = 1e9+7;
vector<ll> FacMod(LIMIT), InvMod(LIMIT), FacInvMod(LIMIT);
const int dpComTableLIMIT = 3e3 + 1;
vector<vector<ll>> Com(dpComTableLIMIT, vector<ll>(dpComTableLIMIT, 0));
const int ComKTableLIMIT = 1e7;
vector<ll> ComK(ComKTableLIMIT);

void DPComInit() {
  // Com[0][j]は0で初期化されている。
  for (int i = 0; i < dpComTableLIMIT; i++) {
    Com[i][0] = 1;
  }

  for (int i = 1; i < dpComTableLIMIT; i++) {
    for (int j = 1; j < dpComTableLIMIT; j++) {
      Com[i][j] = (Com[i - 1][j - 1] + Com[i - 1][j]) % MOD;
    }
  }
}

void ComKInit(ll N) {
  for (int i = 0; i <= ComKTableLIMIT; i++) {
    if (0 < i && i <= N / 2) {
      ComK[i] = (ComK[i - 1] * (N - i + 1) / i) % MOD;
    } else if (i == 0) {
      ComK[i] = 1;
    } else if (N / 2 < i && i <= N) {
      ComK[i] = ComK[N - i];
    } else { // i>Nの時
      ComK[i] = -1;
    }
  }
}

void ComInit() { // tableを作成
  FacMod[0] = FacMod[1] = 1;
  InvMod[0] = 0;
  InvMod[1] = 1; // InvMod[0]は定義できない
  FacInvMod[0] = FacInvMod[1] = 1;

  for (int i = 2; i < LIMIT; i++) {
    FacMod[i] = FacMod[i - 1] * i % MOD;
    InvMod[i] = -InvMod[MOD % i] * (MOD / i) % MOD + MOD;
    FacInvMod[i] = FacInvMod[i - 1] * InvMod[i] % MOD;
  }
}

ll ComMod(int n, int k) {
  if (n >= 0 && k >= 0 && n >= k) {
    return FacMod[n] * (FacInvMod[k] * FacInvMod[n - k] % MOD) % MOD;
  } else {
    return 0; // 戻り値を0にする方が計算結果に影響が少ない。
  }
}

// 繰り返し2乗法
ll power(ll x, ll y) { // 繰り返し2乗法
  if (y < 0) {
    return 0;
  } else if (y == 0) {
    return 1LL;
  } else if (y % 2 == 0) { // 偶数
    return power(x, y / 2) * power(x, y / 2);
  } else { // 奇数
    return power(x, y - 1) * x;
  }
}

// 繰り返し2乗法
ll mpower(ll x, ll y, ll m) { // 繰り返し2乗法
  if (y < 0) {
    return 0;
  } else if (y == 0) {
    return 1LL;
  } else if (y % 2 == 0) { // 偶数
    return mpower(x, y / 2, m) * mpower(x, y / 2, m) % m;
  } else { // 奇数
    return mpower(x, y - 1, m) * x % m;
  }
}

// 互除法
ll GCD(ll a, ll b) { return b ? GCD(b, a % b) : a; }

ll LCM(ll a, ll b) { return (a / GCD(a, b)) * b; }

// 素因数分解
pair<map<ll, ll>, bool> PrimeFactorization(ll N) {
  pair<map<ll, ll>, bool> ret; //<素因数分解,素数判定>
  ret.second = true;

  // 素因数分解
  if (N != 2) {
    while (N % 2 == 0) { // p=2の時。
      N /= 2;
      ret.first[2]++;
      ret.second = false;
    }
  }
  for (ll i = 3; i * i <= N; i += 2) { // p>=3の時。
    while (N % i == 0) {
      N /= i;
      ret.first[i]++;
      ret.second = false;
    }
  }
  if (N != 1) { // Nが素数の時
    ret.first[N]++;
  }

  // 返り値
  return ret;
}

// pair型のソート
bool compare_by_second(pair<ll, ll> a, pair<ll, ll> b) {
  return a.second != b.second ? a.second < b.second : a.first < b.first;
}

class UnionFind {
  vector<int> parent;
  vector<int> rank;
  vector<int> size;

public:
  UnionFind(int N);
  int root(int x);
  void unite(int x, int y);
  bool isUnited(int x, int y);
  int getRank(int x);
  int getSize(int x);
};

UnionFind::UnionFind(int N) : parent(N), rank(N, 1), size(N, 1) {
  for (int i = 0; i < N; i++) {
    parent[i] = i;
  }
}

int UnionFind::root(int x) {
  if (parent[x] == x)
    return x;
  return root(parent[x]);
  /*parent[x] = parent[parent[x]];
  if(parent[x]!=parent[parent[x]]) rank[x]-=1;*/
}

void UnionFind::unite(int x, int y) { // xとyの木を併合
  int rx = root(x);                   // xの根をrx
  int ry = root(y);                   // yの根をry
  // cout << x << " " << y << " " << parent[x] << " " << parent[y] << endl;
  if (rx == ry)
    return; // xとyの根が同じ(=同じ木にある)時はそのまま

  ll xs = size[root(x)];
  ll ys = size[root(y)];
  size[root(x)] += ys;
  size[root(y)] += xs;
  // cout << x << " " << y << " " << size[root(x)] << " " << size[root(y)] <<
  // endl;
  if (rank[x] >= rank[y]) {
    parent[ry] = rx;
    rank[y] += 1;
  } // 大きい木に小さい木が併合される
  else {
    parent[rx] = ry;
    rank[x] += 1;
  } // 根に直接辺を張る
}

bool UnionFind::isUnited(
    int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す
  int rx = root(x);
  int ry = root(y);
  parent[x] = rx;
  parent[y] = ry;
  rank[x] = 2;
  rank[y] = 2;
  return rx == ry;
}

int UnionFind::getRank(int x) { return rank[x]; }

int UnionFind::getSize(int x) { return size[root(x)]; }

bool isOK(ll condition) {
  // return false;
  return true;
}

ll binary_search() {
  // 最小値を求める時
  ll ok = 1e18; // 解が存在する最大値
  ll ng = -1;   // 解が存在しない最小値
  /*
  //最大値を求める時
  ll ok = -1;//解が存在する最小値
  ll ng = 1e18;//解が存在しない最大値
  */

  while (abs(ok - ng) > 1) {
    ll mid = (ok + ng) / 2;
    if (isOK(mid)) {
      ok = mid;
    } else {
      ng = mid;
    }
  }
  return ok;
}

int main() {
  // input
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N, M;
  cin >> N >> M;
  vector<vector<ll>> graph(3 * N);
  vector<ll> u(M), v(M);
  FOR(i, M) {
    ll from, to;
    cin >> from >> to;
    from--;
    to--;
    u[i] = from;
    v[i] = to;
    graph[3 * from].pb(3 * to + 1);
    graph[3 * from + 1].pb(3 * to + 2);
    graph[3 * from + 2].pb(3 * to);
  }
  ll S, T;
  cin >> S >> T;
  S--;
  T--;

  // main
  // bfs
  vector<bool> isSearched(3 * N, false);
  vector<ll> dist(3 * N, 1e9);
  queue<ll> q;
  q.push(3 * S);
  dist[3 * S] = 0;

  while (!q.empty()) {
    ll now = q.front();
    q.pop();
    // if(isSearched[now])continue;
    isSearched[now] = true;
    for (auto next : graph[now]) {
      if (isSearched[next])
        continue;
      if (dist[next] > dist[now] + 1)
        dist[next] = dist[now] + 1;
      q.push(next);
    }
  }

  ll ans = 0;
  if (dist[3 * T] == 1e9) {
    ans = -1;
  } else {
    ans = dist[3 * T] / 3;
  }

  // output
  cout << ans << endl;

  return 0;
}


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

using namespace std;
#define inputInt(a)                                                            \
  int a;                                                                       \
  cin >> a;
#define inputInt2(a, b)                                                        \
  int a;                                                                       \
  int b;                                                                       \
  cin >> a >> b;
#define inputInt3(a, b, c)                                                     \
  int a;                                                                       \
  int b;                                                                       \
  int c;                                                                       \
  cin >> a >> b >> c;
#define inputLong(a)                                                           \
  long a;                                                                      \
  cin >> a;
#define inputIntArray(a, N)                                                    \
  int a[N];                                                                    \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i];                                                               \
  }
#define inputLongArray(a, N)                                                   \
  long a[N];                                                                   \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i];                                                               \
  }
#define inputIntArray2(a, b, N)                                                \
  int a[N];                                                                    \
  int b[N];                                                                    \
  for (int i = 0; i < N; i++) {                                                \
    cin >> a[i] >> b[i];                                                       \
  }
#define output(answer) cout << answer << endl;
#define fN(i, N) for (int i = 0; i < N; i++)
#define fSE(i, s, e) for (int i = s; i <= e; i++)
#define ll long long
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define FOR(i, N) for (int i = 0; i < N; i++)
#define cinv(v, N)                                                             \
  vector<int> v(N);                                                            \
  for (int i = 0; i < N; i++) {                                                \
    cin >> v[i];                                                               \
  }
#define mt make_tuple
#define vll vector<long long int>
#define vvll vector<vector<long long int>>
#define all(v) (v).begin(), (v).end()
#define show(v)                                                                \
  FOR(i, v.size()) { cout << v[i] << " "; }                                    \
  cout << endl;
#define showshow(v)                                                            \
  FOR(i, v.size()) {                                                           \
    FOR(j, v[i].size()) { cout << v[i][j] << " "; }                            \
    cout << endl;                                                              \
  }
const ll MOD = 1e9 + 7;
const ll MOD2 = 998244353;

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;
}

// Combination計算 //ComInitしないと何もできません。
const int LIMIT = 1e6; // 1e6→50ms,1e7→500ms,1e8→5000ms程度。
// const ll MOD = 1e9+7;
vector<ll> FacMod(LIMIT), InvMod(LIMIT), FacInvMod(LIMIT);
const int dpComTableLIMIT = 3e3 + 1;
vector<vector<ll>> Com(dpComTableLIMIT, vector<ll>(dpComTableLIMIT, 0));
const int ComKTableLIMIT = 1e7;
vector<ll> ComK(ComKTableLIMIT);

void DPComInit() {
  // Com[0][j]は0で初期化されている。
  for (int i = 0; i < dpComTableLIMIT; i++) {
    Com[i][0] = 1;
  }

  for (int i = 1; i < dpComTableLIMIT; i++) {
    for (int j = 1; j < dpComTableLIMIT; j++) {
      Com[i][j] = (Com[i - 1][j - 1] + Com[i - 1][j]) % MOD;
    }
  }
}

void ComKInit(ll N) {
  for (int i = 0; i <= ComKTableLIMIT; i++) {
    if (0 < i && i <= N / 2) {
      ComK[i] = (ComK[i - 1] * (N - i + 1) / i) % MOD;
    } else if (i == 0) {
      ComK[i] = 1;
    } else if (N / 2 < i && i <= N) {
      ComK[i] = ComK[N - i];
    } else { // i>Nの時
      ComK[i] = -1;
    }
  }
}

void ComInit() { // tableを作成
  FacMod[0] = FacMod[1] = 1;
  InvMod[0] = 0;
  InvMod[1] = 1; // InvMod[0]は定義できない
  FacInvMod[0] = FacInvMod[1] = 1;

  for (int i = 2; i < LIMIT; i++) {
    FacMod[i] = FacMod[i - 1] * i % MOD;
    InvMod[i] = -InvMod[MOD % i] * (MOD / i) % MOD + MOD;
    FacInvMod[i] = FacInvMod[i - 1] * InvMod[i] % MOD;
  }
}

ll ComMod(int n, int k) {
  if (n >= 0 && k >= 0 && n >= k) {
    return FacMod[n] * (FacInvMod[k] * FacInvMod[n - k] % MOD) % MOD;
  } else {
    return 0; // 戻り値を0にする方が計算結果に影響が少ない。
  }
}

// 繰り返し2乗法
ll power(ll x, ll y) { // 繰り返し2乗法
  if (y < 0) {
    return 0;
  } else if (y == 0) {
    return 1LL;
  } else if (y % 2 == 0) { // 偶数
    return power(x, y / 2) * power(x, y / 2);
  } else { // 奇数
    return power(x, y - 1) * x;
  }
}

// 繰り返し2乗法
ll mpower(ll x, ll y, ll m) { // 繰り返し2乗法
  if (y < 0) {
    return 0;
  } else if (y == 0) {
    return 1LL;
  } else if (y % 2 == 0) { // 偶数
    return mpower(x, y / 2, m) * mpower(x, y / 2, m) % m;
  } else { // 奇数
    return mpower(x, y - 1, m) * x % m;
  }
}

// 互除法
ll GCD(ll a, ll b) { return b ? GCD(b, a % b) : a; }

ll LCM(ll a, ll b) { return (a / GCD(a, b)) * b; }

// 素因数分解
pair<map<ll, ll>, bool> PrimeFactorization(ll N) {
  pair<map<ll, ll>, bool> ret; //<素因数分解,素数判定>
  ret.second = true;

  // 素因数分解
  if (N != 2) {
    while (N % 2 == 0) { // p=2の時。
      N /= 2;
      ret.first[2]++;
      ret.second = false;
    }
  }
  for (ll i = 3; i * i <= N; i += 2) { // p>=3の時。
    while (N % i == 0) {
      N /= i;
      ret.first[i]++;
      ret.second = false;
    }
  }
  if (N != 1) { // Nが素数の時
    ret.first[N]++;
  }

  // 返り値
  return ret;
}

// pair型のソート
bool compare_by_second(pair<ll, ll> a, pair<ll, ll> b) {
  return a.second != b.second ? a.second < b.second : a.first < b.first;
}

class UnionFind {
  vector<int> parent;
  vector<int> rank;
  vector<int> size;

public:
  UnionFind(int N);
  int root(int x);
  void unite(int x, int y);
  bool isUnited(int x, int y);
  int getRank(int x);
  int getSize(int x);
};

UnionFind::UnionFind(int N) : parent(N), rank(N, 1), size(N, 1) {
  for (int i = 0; i < N; i++) {
    parent[i] = i;
  }
}

int UnionFind::root(int x) {
  if (parent[x] == x)
    return x;
  return root(parent[x]);
  /*parent[x] = parent[parent[x]];
  if(parent[x]!=parent[parent[x]]) rank[x]-=1;*/
}

void UnionFind::unite(int x, int y) { // xとyの木を併合
  int rx = root(x);                   // xの根をrx
  int ry = root(y);                   // yの根をry
  // cout << x << " " << y << " " << parent[x] << " " << parent[y] << endl;
  if (rx == ry)
    return; // xとyの根が同じ(=同じ木にある)時はそのまま

  ll xs = size[root(x)];
  ll ys = size[root(y)];
  size[root(x)] += ys;
  size[root(y)] += xs;
  // cout << x << " " << y << " " << size[root(x)] << " " << size[root(y)] <<
  // endl;
  if (rank[x] >= rank[y]) {
    parent[ry] = rx;
    rank[y] += 1;
  } // 大きい木に小さい木が併合される
  else {
    parent[rx] = ry;
    rank[x] += 1;
  } // 根に直接辺を張る
}

bool UnionFind::isUnited(
    int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す
  int rx = root(x);
  int ry = root(y);
  parent[x] = rx;
  parent[y] = ry;
  rank[x] = 2;
  rank[y] = 2;
  return rx == ry;
}

int UnionFind::getRank(int x) { return rank[x]; }

int UnionFind::getSize(int x) { return size[root(x)]; }

bool isOK(ll condition) {
  // return false;
  return true;
}

ll binary_search() {
  // 最小値を求める時
  ll ok = 1e18; // 解が存在する最大値
  ll ng = -1;   // 解が存在しない最小値
  /*
  //最大値を求める時
  ll ok = -1;//解が存在する最小値
  ll ng = 1e18;//解が存在しない最大値
  */

  while (abs(ok - ng) > 1) {
    ll mid = (ok + ng) / 2;
    if (isOK(mid)) {
      ok = mid;
    } else {
      ng = mid;
    }
  }
  return ok;
}

int main() {
  // input
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N, M;
  cin >> N >> M;
  vector<vector<ll>> graph(3 * N);
  vector<ll> u(M), v(M);
  FOR(i, M) {
    ll from, to;
    cin >> from >> to;
    from--;
    to--;
    u[i] = from;
    v[i] = to;
    graph[3 * from].pb(3 * to + 1);
    graph[3 * from + 1].pb(3 * to + 2);
    graph[3 * from + 2].pb(3 * to);
  }
  ll S, T;
  cin >> S >> T;
  S--;
  T--;

  // main
  // bfs
  vector<bool> isSearched(3 * N, false);
  vector<ll> dist(3 * N, 1e9);
  queue<ll> q;
  q.push(3 * S);
  dist[3 * S] = 0;

  while (!q.empty()) {
    ll now = q.front();
    q.pop();
    if (isSearched[now])
      continue;
    isSearched[now] = true;
    for (auto next : graph[now]) {
      if (isSearched[next])
        continue;
      if (dist[next] > dist[now] + 1)
        dist[next] = dist[now] + 1;
      q.push(next);
    }
  }

  ll ans = 0;
  if (dist[3 * T] == 1e9) {
    ans = -1;
  } else {
    ans = dist[3 * T] / 3;
  }

  // output
  cout << ans << endl;

  return 0;
}