Problem p03053 (C++)

Buggy submission (status: Runtime Error):
#pragma region header
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define rev(i, n) for (int i = (int)(n - 1); i >= 0; i--)
#define rev1(i, n) for (int i = (int)(n); i > 0; i--)
#define pb push_back
#define all(v) (v).begin(), (v).end()
#define resort(v) sort((v).rbegin(), (v).rend())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vc vector<char>
#define vvc vector<vector<char>>
#define vb vector<bool>
#define vvb vector<vector<bool>>
using ll = long long;
using P = pair<int, int>;
/* ----------------よく使う数字や配列----------------- */
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
constexpr ll mod = 1e9 + 7;
constexpr ll inf = INT32_MAX / 2;
constexpr ll INF = LLONG_MAX / 2;
constexpr long double eps = DBL_EPSILON;
constexpr long double pi = 3.141592653589793238462643383279;
/* ----------------------end----------------------- */

/* --------------------テンプレート------------------ */
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a <= b) {
    a = b;
    return true;
  }
  return false;
}
/* ----------------------end----------------------- */

/* --------------------ライブラリ-------------------- */
ll fact(int i) { // 階乗
  if (i == 0)
    return 1;
  return (fact(i - 1)) * i % mod;
}
ll gcd(ll a, ll b) { // 最大公約数
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { // 最小公倍数
  return a * b / gcd(a, b);
}
int keta(ll n) { // 桁数を求める
  if (n == 0)
    return 1;
  int count = 0;
  while (n != 0) {
    n /= 10;
    count++;
  }
  return count;
}
ll ketasum(ll n) { // 各桁の和
  ll sum = 0;
  while (n != 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
/* ----------------------end----------------------- */
#pragma endregion
signed main() {
  int h, w;
  cin >> h >> w;
  vvi bo(h, vi(w, -1));
  queue<P> que;
  rep(i, h) {
    rep(j, w) {
      char c;
      cin >> c;
      if (c == '#') {
        que.push({i, j});
        bo[i][j] = 0;
      }
    }
  }
  vi ans;
  while (!que.empty()) {
    P p = que.front();
    que.pop();
    rep(i, 4) {
      int x = p.first + dx[i], y = p.second + dy[i];
      if (x < 0 || x >= h || y < 0 || y >= w || bo[x][y] != -1)
        continue;
      bo[x][y] = bo[p.first][p.second] + 1;
      ans.pb(bo[x][y]);
      que.push({x, y});
    }
  }
  cout << ans.back() << endl;
  return 0;
}

Fixed submission:
#pragma region header
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define rev(i, n) for (int i = (int)(n - 1); i >= 0; i--)
#define rev1(i, n) for (int i = (int)(n); i > 0; i--)
#define pb push_back
#define all(v) (v).begin(), (v).end()
#define resort(v) sort((v).rbegin(), (v).rend())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vc vector<char>
#define vvc vector<vector<char>>
#define vb vector<bool>
#define vvb vector<vector<bool>>
using ll = long long;
using P = pair<int, int>;
/* ----------------よく使う数字や配列----------------- */
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
constexpr ll mod = 1e9 + 7;
constexpr ll inf = INT32_MAX / 2;
constexpr ll INF = LLONG_MAX / 2;
constexpr long double eps = DBL_EPSILON;
constexpr long double pi = 3.141592653589793238462643383279;
/* ----------------------end----------------------- */

/* --------------------テンプレート------------------ */
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a <= b) {
    a = b;
    return true;
  }
  return false;
}
/* ----------------------end----------------------- */

/* --------------------ライブラリ-------------------- */
ll fact(int i) { // 階乗
  if (i == 0)
    return 1;
  return (fact(i - 1)) * i % mod;
}
ll gcd(ll a, ll b) { // 最大公約数
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { // 最小公倍数
  return a * b / gcd(a, b);
}
int keta(ll n) { // 桁数を求める
  if (n == 0)
    return 1;
  int count = 0;
  while (n != 0) {
    n /= 10;
    count++;
  }
  return count;
}
ll ketasum(ll n) { // 各桁の和
  ll sum = 0;
  while (n != 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
/* ----------------------end----------------------- */
#pragma endregion
signed main() {
  int h, w;
  cin >> h >> w;
  vvi bo(h, vi(w, -1));
  queue<P> que;
  rep(i, h) {
    rep(j, w) {
      char c;
      cin >> c;
      if (c == '#') {
        que.push({i, j});
        bo[i][j] = 0;
      }
    }
  }
  vi ans;
  ans.pb(0);
  while (!que.empty()) {
    P p = que.front();
    que.pop();
    rep(i, 4) {
      int x = p.first + dx[i], y = p.second + dy[i];
      if (x < 0 || x >= h || y < 0 || y >= w || bo[x][y] != -1)
        continue;
      bo[x][y] = bo[p.first][p.second] + 1;
      ans.pb(bo[x][y]);
      que.push({x, y});
    }
  }
  cout << ans.back() << endl;
  return 0;
}