Problem p02579 (C++)

Buggy submission (status: Runtime Error):
/* #region Head */

// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll, ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;
using vll = vc<ll>;
using vvll = vvc<ll>;
using vld = vc<ld>;
using vvld = vvc<ld>;
using vs = vc<string>;
using vvs = vvc<string>;
template <class T, class U> using um = unordered_map<T, U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqa = priority_queue<T, vc<T>, greater<T>>;
template <class T> using us = unordered_set<T>;

#define REP(i, m, n) for (ll i = (m), i##_len = (ll)(n); i < i##_len; ++(i))
#define REPM(i, m, n) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; ++(i))
#define REPR(i, m, n) for (ll i = (m), i##_min = (ll)(n); i >= i##_min; --(i))
#define REPD(i, m, n, d)                                                       \
  for (ll i = (m), i##_len = (ll)(n); i < i##_len; i += (d))
#define REPMD(i, m, n, d)                                                      \
  for (ll i = (m), i##_max = (ll)(n); i <= i##_max; i += (d))
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) begin(x), end(x)
#define SIZE(x) ((ll)(x).size())
#define PERM(c)                                                                \
  sort(ALL(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(ALL(c)))
#define UNIQ(v) v.erase(unique(ALL(v)), v.end());

#define endl '\n'
#define sqrt sqrtl
#define floor floorl
#define log2 log2l

constexpr ll INF = 1'010'000'000'000'000'017LL;
constexpr ll MOD = 1'000'000'007LL; // 1e9 + 7
constexpr ld EPS = 1e-12;
constexpr ld PI = 3.14159265358979323846;

template <typename T>
istream &operator>>(istream &is, vc<T> &vec) { // vector 入力
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, vc<T> &vec) { // vector 出力 (for dump)
  os << "{";
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "" : ", ");
  os << "}";
  return os;
}
template <typename T>
ostream &operator>>(ostream &os, vc<T> &vec) { // vector 出力 (inline)
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "\n" : " ");
  return os;
}

template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &pair_var) { // pair 入力
  is >> pair_var.first >> pair_var.second;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) { // pair 出力
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

// map, um, set, us 出力
template <class T> ostream &out_iter(ostream &os, T &map_var) {
  os << "{";
  REPI(itr, map_var) {
    os << *itr;
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  return os << "}";
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T, typename U>
ostream &operator<<(ostream &os, um<T, U> &map_var) {
  os << "{";
  REPI(itr, map_var) {
    auto [key, value] = *itr;
    os << "(" << key << ", " << value << ")";
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, us<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, pq<T> &pq_var) {
  pq<T> pq_cp(pq_var);
  os << "{";
  if (!pq_cp.empty()) {
    os << pq_cp.top(), pq_cp.pop();
    while (!pq_cp.empty())
      os << ", " << pq_cp.top(), pq_cp.pop();
  }
  return os << "}";
}

// dump
#define DUMPOUT cerr
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(move(tail)...);
}

// chmax (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

// chmin (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

// ローカル用
#define DEBUG_

#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

struct AtCoderInitialize {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;
  AtCoderInitialize() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} ATCODER_INITIALIZE;

void Yn(bool p) { cout << (p ? "Yes" : "No") << endl; }
void YN(bool p) { cout << (p ? "YES" : "NO") << endl; }

/* #endregion */

/* #region Graph */

// エッジ（本来エッジは双方向だが，ここでは単方向で管理）
template <class weight_t, class flow_t> struct Edge {
  ll src;          // エッジ始点となる頂点
  ll dst;          // エッジ終点となる頂点
  weight_t weight; // 重み
  flow_t cap;
  Edge() : src(0), dst(0), weight(0) {}
  Edge(ll src, ll dst, weight_t weight) : src(src), dst(dst), weight(weight) {}
  Edge(ll src, ll dst, weight_t weight, flow_t cap)
      : src(src), dst(dst), weight(weight), cap(cap) {}
  // Edge 標準出力
  friend ostream &operator<<(ostream &os, Edge &edge) {
    os << "(" << edge.src << " -> " << edge.dst << ", " << edge.weight << ")";
    return os;
  }
};
// 同じ頂点を始点とするエッジ集合
template <class weight_t, class flow_t>
class Node : public vc<Edge<weight_t, flow_t>> {
public:
  ll idx;
  Node() : vc<Edge<weight_t, flow_t>>() {}
  // void add(int a, int b, weight_t w, flow_t cap) { this->emplace_back(a, b,
  // w, cap); };
};
// graph[i] := 頂点 i を始点とするエッジ集合
template <class weight_t, class flow_t>
class Graph : public vc<Node<weight_t, flow_t>> {
public:
  Graph() : vc<Node<weight_t, flow_t>>() {}
  Graph(int n) : vc<Node<weight_t, flow_t>>(n) {
    REP(i, 0, n)(*this)[i].idx = i;
  }
  // 単方向
  void add_arc(int a, int b, weight_t w = 1, flow_t cap = 1) {
    (*this)[a].emplace_back(a, b, w, cap);
  }
  // 双方向
  void add_edge(int a, int b, weight_t w = 1, flow_t cap = 1) {
    add_arc(a, b, w, cap), add_arc(b, a, w, cap);
  }
};
// using Array = vc<Weight>;
// using Matrix = vc<Array>;

/* #endregion */

// Problem
void solve() {
  ll h, w;
  cin >> h >> w;
  ll ch, cw, dh, dw;
  cin >> ch >> cw >> dh >> dw;
  --ch, --cw, --dh, --dw;
  vc<string> s(h);
  cin >> s;

  char wall = '#';
  const int dCol[4] = {1, 0, -1, 0};
  const int dRow[4] = {0, 1, 0, -1};
  vvll groupnums(h, vll(w, -1));
  // auto dfs = [&](auto &&dfs, ll num, ll curRow, ll curCol) -> void {
  //     if (groupnums[curRow][curCol] == num) return; // 訪問済み
  //     if (s[curRow][curCol] == wall) return;
  //     groupnums[curRow][curCol] = num;
  //     // for (Edge<ll, ll> &edge : graph[idx]) dfs(dfs, num, edge.dst);
  //     REP(dir, 0, 4) {
  //         ll nextRow = curRow + dRow[dir];
  //         ll nextCol = curCol + dCol[dir];
  //         if (nextRow < 0 || nextRow >= h || nextCol < 0 || nextCol >= w)
  //         continue; if (s[nextRow][nextCol] == wall) continue;
  //         // if (dist[nextRow][nextCol] != INF) continue; // 訪問済み（BFS）
  //         dfs(dfs, num, nextRow, nextCol);
  //     }
  // };
  ll num = 0;
  using node = pll;
  // REP(i, 0, h) REP(j, 0, w) if (groupnums[i][j] == -1 && s[i][j] != wall)
  // dfs(dfs, num++, i, j);
  REP(sRow, 0, h)
  REP(sCol, 0, w) if (groupnums[sRow][sCol] == -1 && s[sRow][sCol] != wall) {
    groupnums[sRow][sCol] = num;
    queue<node> que;
    que.emplace(sRow, sCol);

    while (!que.empty()) {
      auto [curRow, curCol] = que.front();
      que.pop();
      // Dist curDist = dist[curRow][curCol];

      // cuerrent から辿れる頂点をすべて調べる
      REP(dir, 0, 4) {
        ll nextRow = curRow + dRow[dir];
        ll nextCol = curCol + dCol[dir];
        if (nextRow < 0 || nextRow >= h || nextCol < 0 || nextCol >= w)
          continue;
        if (s[nextRow][nextCol] == wall)
          continue;
        if (groupnums[nextRow][nextCol] != -1)
          continue; // 訪問済み（BFS）

        // Dist nextDist = curDist + 1;
        // if (chmin(dist[nextRow][nextCol], nextDist)) que.emplace(nextRow,
        // nextCol); // ↑この書き方はダイクストラっぽい
        groupnums[nextRow][nextCol] = num;
        que.emplace(nextRow, nextCol);
      }
    }
    num++;
  }
  // BFS 終了

  // dump(groupnums, num); // num に連結成分数が入っている
  if (groupnums[ch][cw] == groupnums[dh][dw]) {
    cout << 0 << endl;
    return;
  }
  // 1回以上ワープする

  // vc<vc<bool>> warpable(num, vc<bool>(num, false));
  // dump(groupnums);
  set<pll> arcs;

  // 左右の隣同士
  REP(i, 0, h) REP(j, 0, w) if (groupnums[i][j] != -1) {
    REPM(k, -2, 2) REPM(l, 0, 2) {
      ll ii = i + k;
      ll jj = j + l;
      if (ii < 0 || jj < 0 || ii >= h || jj >= w)
        continue;
      if (groupnums[ii][jj] == -1)
        continue;
      if (groupnums[ii][jj] == groupnums[i][j])
        continue;
      // warpable[groupnums[i][j]][groupnums[ii][jj]] = true;
      // warpable[groupnums[ii][jj]][groupnums[i][j]] = true;
      arcs.emplace(groupnums[i][j], groupnums[ii][jj]);
      arcs.emplace(groupnums[ii][jj], groupnums[i][j]);
    }
    // REPM(k, -1, 1) REPM(l, -1, 1) {
    //     if (k == 0 && l == 0) continue;
    // }
  }
  // dump(warpable);
  assert(false);

  Graph<ll, ll> graph(num);
  // REP(i, 0, num) REP(j, 0, num) if (warpable[i][j]) graph.add_arc(i, j);
  for (const pll &p : arcs)
    graph.add_arc(p.first, p.second);

  ll idx1 = groupnums[ch][cw]; // 始点として選ぶ頂点
  // if (SIZE(graph[idx1]) == 0) continue;

  using Weight = ll;
  using state = pair<Weight, ll>; // (始点からの最短経路長, ノード番号)
  priority_queue<state, vc<state>, greater<state>>
      que; // 昇順に並べ替え，小さい順に取り出す
  vc<Weight> dist(num, INF);
  dist[idx1] = 0;
  que.emplace(0, idx1);
  while (que.size()) {
    // tie(d, v) = que.top();
    state cur = que.top();
    que.pop();
    Weight d = cur.first;
    ll v = cur.second;

    if (dist[v] < d)
      continue;
    for (Edge<Weight, ll> edge : graph[v])
      if (chmin(dist[edge.dst], dist[v] + edge.weight))
        que.emplace(dist[edge.dst], edge.dst);
  }
  // ここまでで， idx1 を始点として各頂点までの距離が dist に入った
  // ただし，到達不可能な頂点は距離が INF になっているので，
  // chmax(ret, *max_element(ALL(dist))); は不可

  if (dist[groupnums[dh][dw]] == INF) {
    cout << -1 << endl;
  } else {
    cout << dist[groupnums[dh][dw]] << endl;
  }
}

// entry point
int main() {
  solve();
  return 0;
}


Fixed submission:
/* #region Head */

// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll, ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;
using vll = vc<ll>;
using vvll = vvc<ll>;
using vld = vc<ld>;
using vvld = vvc<ld>;
using vs = vc<string>;
using vvs = vvc<string>;
template <class T, class U> using um = unordered_map<T, U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqa = priority_queue<T, vc<T>, greater<T>>;
template <class T> using us = unordered_set<T>;

#define REP(i, m, n) for (ll i = (m), i##_len = (ll)(n); i < i##_len; ++(i))
#define REPM(i, m, n) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; ++(i))
#define REPR(i, m, n) for (ll i = (m), i##_min = (ll)(n); i >= i##_min; --(i))
#define REPD(i, m, n, d)                                                       \
  for (ll i = (m), i##_len = (ll)(n); i < i##_len; i += (d))
#define REPMD(i, m, n, d)                                                      \
  for (ll i = (m), i##_max = (ll)(n); i <= i##_max; i += (d))
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) begin(x), end(x)
#define SIZE(x) ((ll)(x).size())
#define PERM(c)                                                                \
  sort(ALL(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(ALL(c)))
#define UNIQ(v) v.erase(unique(ALL(v)), v.end());

#define endl '\n'
#define sqrt sqrtl
#define floor floorl
#define log2 log2l

constexpr ll INF = 1'010'000'000'000'000'017LL;
constexpr ll MOD = 1'000'000'007LL; // 1e9 + 7
constexpr ld EPS = 1e-12;
constexpr ld PI = 3.14159265358979323846;

template <typename T>
istream &operator>>(istream &is, vc<T> &vec) { // vector 入力
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, vc<T> &vec) { // vector 出力 (for dump)
  os << "{";
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "" : ", ");
  os << "}";
  return os;
}
template <typename T>
ostream &operator>>(ostream &os, vc<T> &vec) { // vector 出力 (inline)
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "\n" : " ");
  return os;
}

template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &pair_var) { // pair 入力
  is >> pair_var.first >> pair_var.second;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) { // pair 出力
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

// map, um, set, us 出力
template <class T> ostream &out_iter(ostream &os, T &map_var) {
  os << "{";
  REPI(itr, map_var) {
    os << *itr;
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  return os << "}";
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T, typename U>
ostream &operator<<(ostream &os, um<T, U> &map_var) {
  os << "{";
  REPI(itr, map_var) {
    auto [key, value] = *itr;
    os << "(" << key << ", " << value << ")";
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  os << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, us<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, pq<T> &pq_var) {
  pq<T> pq_cp(pq_var);
  os << "{";
  if (!pq_cp.empty()) {
    os << pq_cp.top(), pq_cp.pop();
    while (!pq_cp.empty())
      os << ", " << pq_cp.top(), pq_cp.pop();
  }
  return os << "}";
}

// dump
#define DUMPOUT cerr
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(move(tail)...);
}

// chmax (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

// chmin (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

// ローカル用
#define DEBUG_

#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

struct AtCoderInitialize {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;
  AtCoderInitialize() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} ATCODER_INITIALIZE;

void Yn(bool p) { cout << (p ? "Yes" : "No") << endl; }
void YN(bool p) { cout << (p ? "YES" : "NO") << endl; }

/* #endregion */

/* #region Graph */

// エッジ（本来エッジは双方向だが，ここでは単方向で管理）
template <class weight_t, class flow_t> struct Edge {
  ll src;          // エッジ始点となる頂点
  ll dst;          // エッジ終点となる頂点
  weight_t weight; // 重み
  flow_t cap;
  Edge() : src(0), dst(0), weight(0) {}
  Edge(ll src, ll dst, weight_t weight) : src(src), dst(dst), weight(weight) {}
  Edge(ll src, ll dst, weight_t weight, flow_t cap)
      : src(src), dst(dst), weight(weight), cap(cap) {}
  // Edge 標準出力
  friend ostream &operator<<(ostream &os, Edge &edge) {
    os << "(" << edge.src << " -> " << edge.dst << ", " << edge.weight << ")";
    return os;
  }
};
// 同じ頂点を始点とするエッジ集合
template <class weight_t, class flow_t>
class Node : public vc<Edge<weight_t, flow_t>> {
public:
  ll idx;
  Node() : vc<Edge<weight_t, flow_t>>() {}
  // void add(int a, int b, weight_t w, flow_t cap) { this->emplace_back(a, b,
  // w, cap); };
};
// graph[i] := 頂点 i を始点とするエッジ集合
template <class weight_t, class flow_t>
class Graph : public vc<Node<weight_t, flow_t>> {
public:
  Graph() : vc<Node<weight_t, flow_t>>() {}
  Graph(int n) : vc<Node<weight_t, flow_t>>(n) {
    REP(i, 0, n)(*this)[i].idx = i;
  }
  // 単方向
  void add_arc(int a, int b, weight_t w = 1, flow_t cap = 1) {
    (*this)[a].emplace_back(a, b, w, cap);
  }
  // 双方向
  void add_edge(int a, int b, weight_t w = 1, flow_t cap = 1) {
    add_arc(a, b, w, cap), add_arc(b, a, w, cap);
  }
};
// using Array = vc<Weight>;
// using Matrix = vc<Array>;

/* #endregion */

// Problem
void solve() {
  ll h, w;
  cin >> h >> w;
  ll ch, cw, dh, dw;
  cin >> ch >> cw >> dh >> dw;
  --ch, --cw, --dh, --dw;
  vc<string> s(h);
  cin >> s;

  char wall = '#';
  const int dCol[4] = {1, 0, -1, 0};
  const int dRow[4] = {0, 1, 0, -1};
  vvll groupnums(h, vll(w, -1));
  // auto dfs = [&](auto &&dfs, ll num, ll curRow, ll curCol) -> void {
  //     if (groupnums[curRow][curCol] == num) return; // 訪問済み
  //     if (s[curRow][curCol] == wall) return;
  //     groupnums[curRow][curCol] = num;
  //     // for (Edge<ll, ll> &edge : graph[idx]) dfs(dfs, num, edge.dst);
  //     REP(dir, 0, 4) {
  //         ll nextRow = curRow + dRow[dir];
  //         ll nextCol = curCol + dCol[dir];
  //         if (nextRow < 0 || nextRow >= h || nextCol < 0 || nextCol >= w)
  //         continue; if (s[nextRow][nextCol] == wall) continue;
  //         // if (dist[nextRow][nextCol] != INF) continue; // 訪問済み（BFS）
  //         dfs(dfs, num, nextRow, nextCol);
  //     }
  // };
  ll num = 0;
  using node = pll;
  // REP(i, 0, h) REP(j, 0, w) if (groupnums[i][j] == -1 && s[i][j] != wall)
  // dfs(dfs, num++, i, j);
  REP(sRow, 0, h)
  REP(sCol, 0, w) if (groupnums[sRow][sCol] == -1 && s[sRow][sCol] != wall) {
    groupnums[sRow][sCol] = num;
    queue<node> que;
    que.emplace(sRow, sCol);

    while (!que.empty()) {
      auto [curRow, curCol] = que.front();
      que.pop();
      // Dist curDist = dist[curRow][curCol];

      // cuerrent から辿れる頂点をすべて調べる
      REP(dir, 0, 4) {
        ll nextRow = curRow + dRow[dir];
        ll nextCol = curCol + dCol[dir];
        if (nextRow < 0 || nextRow >= h || nextCol < 0 || nextCol >= w)
          continue;
        if (s[nextRow][nextCol] == wall)
          continue;
        if (groupnums[nextRow][nextCol] != -1)
          continue; // 訪問済み（BFS）

        // Dist nextDist = curDist + 1;
        // if (chmin(dist[nextRow][nextCol], nextDist)) que.emplace(nextRow,
        // nextCol); // ↑この書き方はダイクストラっぽい
        groupnums[nextRow][nextCol] = num;
        que.emplace(nextRow, nextCol);
      }
    }
    num++;
  }
  // BFS 終了

  // dump(groupnums, num); // num に連結成分数が入っている
  if (groupnums[ch][cw] == groupnums[dh][dw]) {
    cout << 0 << endl;
    return;
  }
  // 1回以上ワープする

  // vc<vc<bool>> warpable(num, vc<bool>(num, false));
  // dump(groupnums);
  set<pll> arcs;

  // 左右の隣同士
  REP(i, 0, h) REP(j, 0, w) if (groupnums[i][j] != -1) {
    REPM(k, -2, 2) REPM(l, 0, 2) {
      ll ii = i + k;
      ll jj = j + l;
      if (ii < 0 || jj < 0 || ii >= h || jj >= w)
        continue;
      if (groupnums[ii][jj] == -1)
        continue;
      if (groupnums[ii][jj] == groupnums[i][j])
        continue;
      // warpable[groupnums[i][j]][groupnums[ii][jj]] = true;
      // warpable[groupnums[ii][jj]][groupnums[i][j]] = true;
      arcs.emplace(groupnums[i][j], groupnums[ii][jj]);
      arcs.emplace(groupnums[ii][jj], groupnums[i][j]);
    }
    // REPM(k, -1, 1) REPM(l, -1, 1) {
    //     if (k == 0 && l == 0) continue;
    // }
  }
  // dump(warpable);
  // assert(false);

  Graph<ll, ll> graph(num);
  // REP(i, 0, num) REP(j, 0, num) if (warpable[i][j]) graph.add_arc(i, j);
  for (const pll &p : arcs)
    graph.add_arc(p.first, p.second);

  ll idx1 = groupnums[ch][cw]; // 始点として選ぶ頂点
  // if (SIZE(graph[idx1]) == 0) continue;

  using Weight = ll;
  using state = pair<Weight, ll>; // (始点からの最短経路長, ノード番号)
  priority_queue<state, vc<state>, greater<state>>
      que; // 昇順に並べ替え，小さい順に取り出す
  vc<Weight> dist(num, INF);
  dist[idx1] = 0;
  que.emplace(0, idx1);
  while (que.size()) {
    // tie(d, v) = que.top();
    state cur = que.top();
    que.pop();
    Weight d = cur.first;
    ll v = cur.second;

    if (dist[v] < d)
      continue;
    for (Edge<Weight, ll> edge : graph[v])
      if (chmin(dist[edge.dst], dist[v] + edge.weight))
        que.emplace(dist[edge.dst], edge.dst);
  }
  // ここまでで， idx1 を始点として各頂点までの距離が dist に入った
  // ただし，到達不可能な頂点は距離が INF になっているので，
  // chmax(ret, *max_element(ALL(dist))); は不可

  if (dist[groupnums[dh][dw]] == INF) {
    cout << -1 << endl;
  } else {
    cout << dist[groupnums[dh][dw]] << endl;
  }
}

// entry point
int main() {
  solve();
  return 0;
}