Problem p03436 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <sys/time.h>
using namespace std;

#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define repi(i, a, b)                                                          \
  for (long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template <class T1, class T2> bool chmin(T1 &a, T2 b) {
  return b < a && (a = b, true);
}
template <class T1, class T2> bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using P = pair<ll, ll>;
using ld = long double;
using vld = vector<ld>;
using vi = vector<int>;
using vvi = vector<vi>;
vll conv(vi &v) {
  vll r(v.size());
  rep(i, v.size()) r[i] = v[i];
  return r;
}

inline void input(int &v) {
  v = 0;
  char c = 0;
  int p = 1;
  while (c < '0' || c > '9') {
    if (c == '-')
      p = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    v = (v << 3) + (v << 1) + c - '0';
    c = getchar();
  }
  v *= p;
} // これを使うならば、tieとかを消して！！
template <typename T, typename U>
ostream &operator<<(ostream &o, const pair<T, U> &v) {
  o << "(" << v.first << ", " << v.second << ")";
  return o;
}
template <size_t...> struct seq {};
template <size_t N, size_t... Is>
struct gen_seq : gen_seq<N - 1, N - 1, Is...> {};
template <size_t... Is> struct gen_seq<0, Is...> : seq<Is...> {};
template <class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch, Tr> &os, Tuple const &t, seq<Is...>) {
  using s = int[];
  (void)s{0, (void(os << (Is == 0 ? "" : ", ") << get<Is>(t)), 0)...};
}
template <class Ch, class Tr, class... Args>
auto operator<<(basic_ostream<Ch, Tr> &os, tuple<Args...> const &t)
    -> basic_ostream<Ch, Tr> & {
  os << "(";
  print_tuple(os, t, gen_seq<sizeof...(Args)>());
  return os << ")";
}
ostream &operator<<(ostream &o, const vvll &v) {
  rep(i, v.size()) {
    rep(j, v[i].size()) o << v[i][j] << " ";
    o << endl;
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const deque<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T>
ostream &operator<<(ostream &o, const unordered_set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U, typename V>
ostream &operator<<(ostream &o, const unordered_map<T, U, V> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it;
  o << "]";
  return o;
}
vector<int> range(const int x, const int y) {
  vector<int> v(y - x + 1);
  iota(v.begin(), v.end(), x);
  return v;
}
template <typename T> istream &operator>>(istream &i, vector<T> &o) {
  rep(j, o.size()) i >> o[j];
  return i;
}
template <typename T, typename S, typename U>
ostream &operator<<(ostream &o, const priority_queue<T, S, U> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.top();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const queue<T> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.front();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const stack<T> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.top();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> unordered_map<T, ll> counter(vector<T> vec) {
  unordered_map<T, ll> ret;
  for (auto &&x : vec)
    ret[x]++;
  return ret;
};
string substr(string s, P x) { return s.substr(x.fi, x.se - x.fi); }
void vizGraph(vvll &g, int mode = 0, string filename = "out.png") {
  ofstream ofs("./out.dot");
  ofs << "digraph graph_name {" << endl;
  set<P> memo;
  rep(i, g.size()) rep(j, g[i].size()) {
    if (mode && (memo.count(P(i, g[i][j])) || memo.count(P(g[i][j], i))))
      continue;
    memo.insert(P(i, g[i][j]));
    ofs << "    " << i << " -> " << g[i][j]
        << (mode ? " [arrowhead = none]" : "") << endl;
  }
  ofs << "}" << endl;
  ofs.close();
  system(((string) "dot -T png out.dot >" + filename).c_str());
}
size_t random_seed;
namespace std {
using argument_type = P;
template <> struct hash<argument_type> {
  size_t operator()(argument_type const &x) const {
    size_t seed = random_seed;
    seed ^= hash<ll>{}(x.fi);
    seed ^= (hash<ll>{}(x.se) << 1);
    return seed;
  }
};
}; // namespace std
struct timeval start;
double sec() {
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return (tv.tv_sec - start.tv_sec) + (tv.tv_usec - start.tv_usec) * 1e-6;
}
struct init_ {
  init_() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    gettimeofday(&start, NULL);
    struct timeval myTime;
    struct tm *time_st;
    gettimeofday(&myTime, NULL);
    time_st = localtime(&myTime.tv_sec);
    srand(myTime.tv_usec);
    random_seed = RAND_MAX / 2 + rand() / 2;
  }
} init__;
#define ldout fixed << setprecision(40)

#define EPS (double)1e-14
#define INF (ll)1e18
#define mo (ll)(1e9 + 7)

int main(void) {
  ll h, w;
  cin >> h >> w;
  vector<string> s(h);
  cin >> s;
  ll cnt = 0;
  rep(hh, h) rep(ww, w) { cnt += s[hh][ww] == '#'; }
  vector<P> q, q_next;
  q.pb(P(0, 0));
  vvll dist(h, vll(w, INF));
  ll cyc = 0;
  while (q.size()) {
    for (auto x : q) {
      ll i = x.fi, j = x.se;
      if (dist[i][j] != INF)
        continue;
      dist[i][j] = cyc;
      if (dist[h - 1][w - 1] != INF) {
        cout << h * w - dist[h - 1][w - 1] - 1 - cnt << endl;
        return 0;
      }

      vll dx = {1, -1, 0, 0};
      vll dy = {0, 0, 1, -1};
      rep(d, 4) {
        ll ii = i + dx[d];
        ll jj = j + dy[d];
        if (ii < 0 || ii >= h)
          continue;
        if (jj < 0 || jj >= w)
          continue;
        if (s[ii][jj] == '#')
          continue;
        q_next.pb(P(ii, jj));
      }
    }
    cyc++;
    swap(q, q_next);
  }
  cout << -1 << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#include <sys/time.h>
using namespace std;

#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define repi(i, a, b)                                                          \
  for (long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template <class T1, class T2> bool chmin(T1 &a, T2 b) {
  return b < a && (a = b, true);
}
template <class T1, class T2> bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using P = pair<ll, ll>;
using ld = long double;
using vld = vector<ld>;
using vi = vector<int>;
using vvi = vector<vi>;
vll conv(vi &v) {
  vll r(v.size());
  rep(i, v.size()) r[i] = v[i];
  return r;
}

inline void input(int &v) {
  v = 0;
  char c = 0;
  int p = 1;
  while (c < '0' || c > '9') {
    if (c == '-')
      p = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    v = (v << 3) + (v << 1) + c - '0';
    c = getchar();
  }
  v *= p;
} // これを使うならば、tieとかを消して！！
template <typename T, typename U>
ostream &operator<<(ostream &o, const pair<T, U> &v) {
  o << "(" << v.first << ", " << v.second << ")";
  return o;
}
template <size_t...> struct seq {};
template <size_t N, size_t... Is>
struct gen_seq : gen_seq<N - 1, N - 1, Is...> {};
template <size_t... Is> struct gen_seq<0, Is...> : seq<Is...> {};
template <class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch, Tr> &os, Tuple const &t, seq<Is...>) {
  using s = int[];
  (void)s{0, (void(os << (Is == 0 ? "" : ", ") << get<Is>(t)), 0)...};
}
template <class Ch, class Tr, class... Args>
auto operator<<(basic_ostream<Ch, Tr> &os, tuple<Args...> const &t)
    -> basic_ostream<Ch, Tr> & {
  os << "(";
  print_tuple(os, t, gen_seq<sizeof...(Args)>());
  return os << ")";
}
ostream &operator<<(ostream &o, const vvll &v) {
  rep(i, v.size()) {
    rep(j, v[i].size()) o << v[i][j] << " ";
    o << endl;
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const deque<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T>
ostream &operator<<(ostream &o, const unordered_set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U, typename V>
ostream &operator<<(ostream &o, const unordered_map<T, U, V> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it;
  o << "]";
  return o;
}
vector<int> range(const int x, const int y) {
  vector<int> v(y - x + 1);
  iota(v.begin(), v.end(), x);
  return v;
}
template <typename T> istream &operator>>(istream &i, vector<T> &o) {
  rep(j, o.size()) i >> o[j];
  return i;
}
template <typename T, typename S, typename U>
ostream &operator<<(ostream &o, const priority_queue<T, S, U> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.top();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const queue<T> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.front();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const stack<T> &v) {
  auto tmp = v;
  while (tmp.size()) {
    auto x = tmp.top();
    tmp.pop();
    o << x << " ";
  }
  return o;
}
template <typename T> unordered_map<T, ll> counter(vector<T> vec) {
  unordered_map<T, ll> ret;
  for (auto &&x : vec)
    ret[x]++;
  return ret;
};
string substr(string s, P x) { return s.substr(x.fi, x.se - x.fi); }
void vizGraph(vvll &g, int mode = 0, string filename = "out.png") {
  ofstream ofs("./out.dot");
  ofs << "digraph graph_name {" << endl;
  set<P> memo;
  rep(i, g.size()) rep(j, g[i].size()) {
    if (mode && (memo.count(P(i, g[i][j])) || memo.count(P(g[i][j], i))))
      continue;
    memo.insert(P(i, g[i][j]));
    ofs << "    " << i << " -> " << g[i][j]
        << (mode ? " [arrowhead = none]" : "") << endl;
  }
  ofs << "}" << endl;
  ofs.close();
  system(((string) "dot -T png out.dot >" + filename).c_str());
}
size_t random_seed;
namespace std {
using argument_type = P;
template <> struct hash<argument_type> {
  size_t operator()(argument_type const &x) const {
    size_t seed = random_seed;
    seed ^= hash<ll>{}(x.fi);
    seed ^= (hash<ll>{}(x.se) << 1);
    return seed;
  }
};
}; // namespace std
struct timeval start;
double sec() {
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return (tv.tv_sec - start.tv_sec) + (tv.tv_usec - start.tv_usec) * 1e-6;
}
struct init_ {
  init_() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    gettimeofday(&start, NULL);
    struct timeval myTime;
    struct tm *time_st;
    gettimeofday(&myTime, NULL);
    time_st = localtime(&myTime.tv_sec);
    srand(myTime.tv_usec);
    random_seed = RAND_MAX / 2 + rand() / 2;
  }
} init__;
#define ldout fixed << setprecision(40)

#define EPS (double)1e-14
#define INF (ll)1e18
#define mo (ll)(1e9 + 7)

int main(void) {
  ll h, w;
  cin >> h >> w;
  vector<string> s(h);
  cin >> s;
  ll cnt = 0;
  rep(hh, h) rep(ww, w) { cnt += s[hh][ww] == '#'; }
  vector<P> q, q_next;
  q.pb(P(0, 0));
  vvll dist(h, vll(w, INF));
  ll cyc = 0;
  while (q.size()) {
    q_next.clear();
    for (auto x : q) {
      ll i = x.fi, j = x.se;
      if (dist[i][j] != INF)
        continue;
      dist[i][j] = cyc;
      if (dist[h - 1][w - 1] != INF) {
        cout << h * w - dist[h - 1][w - 1] - 1 - cnt << endl;
        return 0;
      }

      vll dx = {1, -1, 0, 0};
      vll dy = {0, 0, 1, -1};
      rep(d, 4) {
        ll ii = i + dx[d];
        ll jj = j + dy[d];
        if (ii < 0 || ii >= h)
          continue;
        if (jj < 0 || jj >= w)
          continue;
        if (s[ii][jj] == '#')
          continue;
        q_next.pb(P(ii, jj));
      }
    }
    cyc++;
    swap(q, q_next);
  }
  cout << -1 << endl;

  return 0;
}