Problem p03053 (C++)

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

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))
#define sz(v) ((int)v.size())

using namespace std;

using i64 = long long;
using f80 = long double;
using vi32 = vector<int>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() {
  cout << "Yes" << endl;
  exit(0);
}
inline void no() {
  cout << "No" << endl;
  exit(0);
}
inline i64 gcd(i64 a, i64 b) {
  if (min(a, b) == 0)
    return max(a, b);
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
inline i64 lcm(i64 a, i64 b) {
  if (min(a, b) == 0)
    return max(a, b);
  return a / gcd(a, b) * b;
}
template <typename T>
class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T>
class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { x = max(x, y); }
template <typename T> inline void amin(T &x, T y) { x = min(x, y); }
template <typename T> inline T exp(T x, i64 n, T e = 1) {
  T r = e;
  while (n > 0) {
    if (n & 1)
      r *= x;
    x *= x;
    n >>= 1;
  }
  return r;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  each(x, v) is >> x;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  rep(i, v.size()) {
    if (i)
      os << ' ';
    os << v[i];
  }
  return os;
}
void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(16);
  solve();
  return 0;
}

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};

void solve() {
  int h, w;
  cin >> h >> w;
  vstr s(h);
  cin >> s;
  using P = tuple<int, int, int>;
  queue<P> q;
  vector<vi32> dp(h, vi32(w, 1e9));
  rep(i, h) rep(j, w) {
    if (s[i][j] == '#') {
      dp[i][j] = 0;
      q.emplace(i, j, 0);
    }
  }
  while (q.size()) {
    int x, y, c;
    tie(x, y, c) = q.front();
    q.pop();
    if (dp[x][y] < c) {
      continue;
    }
    rep(i, 4) {
      int wx = x + dx[i];
      int wy = y + dy[i];
      if (wx < 0 || wx >= h || wy < 0 || wy >= w)
        continue;
      if (dp[wx][wy] <= c)
        continue;
      dp[wx][wy] = c + 1;
      q.emplace(wx, wy, c + 1);
    }
  }
  int ans = 0;
  rep(i, h) rep(j, w) { amax(ans, dp[i][j]); }
  cout << ans << endl;
}


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

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))
#define sz(v) ((int)v.size())

using namespace std;

using i64 = long long;
using f80 = long double;
using vi32 = vector<int>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() {
  cout << "Yes" << endl;
  exit(0);
}
inline void no() {
  cout << "No" << endl;
  exit(0);
}
inline i64 gcd(i64 a, i64 b) {
  if (min(a, b) == 0)
    return max(a, b);
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
inline i64 lcm(i64 a, i64 b) {
  if (min(a, b) == 0)
    return max(a, b);
  return a / gcd(a, b) * b;
}
template <typename T>
class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T>
class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { x = max(x, y); }
template <typename T> inline void amin(T &x, T y) { x = min(x, y); }
template <typename T> inline T exp(T x, i64 n, T e = 1) {
  T r = e;
  while (n > 0) {
    if (n & 1)
      r *= x;
    x *= x;
    n >>= 1;
  }
  return r;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  each(x, v) is >> x;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  rep(i, v.size()) {
    if (i)
      os << ' ';
    os << v[i];
  }
  return os;
}
void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(16);
  solve();
  return 0;
}

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};

void solve() {
  int h, w;
  cin >> h >> w;
  vstr s(h);
  cin >> s;
  using P = tuple<int, int, int>;
  queue<P> q;
  vector<vi32> dp(h, vi32(w, 1e9));
  rep(i, h) rep(j, w) {
    if (s[i][j] == '#') {
      dp[i][j] = 0;
      q.emplace(i, j, 0);
    }
  }
  while (q.size()) {
    int x, y, c;
    tie(x, y, c) = q.front();
    q.pop();
    if (dp[x][y] < c) {
      continue;
    }
    rep(i, 4) {
      int wx = x + dx[i];
      int wy = y + dy[i];
      if (wx < 0 || wx >= h || wy < 0 || wy >= w)
        continue;
      if (dp[wx][wy] <= c + 1)
        continue;
      dp[wx][wy] = c + 1;
      q.emplace(wx, wy, c + 1);
    }
  }
  int ans = 0;
  rep(i, h) rep(j, w) { amax(ans, dp[i][j]); }
  cout << ans << endl;
}