Problem p03725 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(), (x).end()
using ll = long long;
using ld = long double;
#define vpl vector<pair<long long, long long>>
#define vl vector<long long>
#define vvl vector<vector<long long>>
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define rep2(i, s, n) for (ll i = (s); i < (ll)(n); i++)
using pll = pair<long long, long long>;
#define cY cout << "Yes" << endl
#define cN cout << "No" << endl
const long long INF = 1LL << 60;
long long MOD = 1000000007;
const long double pi = 3.1415926535897932;
#define pb push_back
#define mp make_pair
#define mt make_tuple
using Grid = vector<vector<char>>;
#define vc vector<char>
//(mod m)でのaの逆元を計算する
// a/b(mod m)=a(mod m)*modinv(b,m)
long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

// 最大最小の入れ替え
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;
}

// 約数列挙
vector<long long> divisor(long long n) {
  vector<long long> ret;
  for (long long i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end()); // 昇順に並べる
  return ret;
}
// コンビネーション
ll nCr(ll n, ll r) {
  ll ans = 1;
  for (ll i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (ll i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}
// 素因数分解
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

// 切り上げの割り算は(a + b - 1) / bでできる

// ここから
int main() {
  ll H, W, K;
  cin >> H >> W >> K;
  Grid G(W, vc(H));
  ll sx, sy;
  rep(i, H) {
    rep(j, W) {
      cin >> G[j][i];
      if (G[j][i] == 'S') {
        sx = j;
        sy = i;
      }
    }
  }
  ll dist = INF;
  vector<vector<bool>> visit(W, vector<bool>(H, false));
  queue<pll> q;
  pll w = mp(sx, sy);
  q.push(w);
  map<pll, ll> D;
  D[w] = 0;
  ll dx[4] = {1, 0, -1, 0};
  ll dy[4] = {0, 1, 0, -1};
  visit[sx][sy] = true;
  while (!q.empty()) {
    pll P = q.front();
    q.pop();
    ll x = P.first;
    ll y = P.second;
    dist = min({dist, x, W - x - 1, y, H - y - 1});
    visit[x][y] = true;
    if (D[P] == K)
      continue;
    rep(i, 4) {
      ll nx = x + dx[i];
      ll ny = y + dy[i];
      if (nx < 0 || ny < 0 || ny > H - 1 || nx > W - 1 || visit[nx][ny])
        continue;
      if (G[nx][ny] == '.') {
        if (nx == 0 || nx == W - 1 || ny == H - 1 || ny == 0) {
          cout << 1 << endl;
          return 0;
        } else {
          pll p = mp(nx, ny);
          q.push(p);
          D[p] = D[P] + 1;
        }
      }
    }
  }
  cout << 1 + (dist + K - 1) / K << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(), (x).end()
using ll = long long;
using ld = long double;
#define vpl vector<pair<long long, long long>>
#define vl vector<long long>
#define vvl vector<vector<long long>>
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define rep2(i, s, n) for (ll i = (s); i < (ll)(n); i++)
using pll = pair<long long, long long>;
#define cY cout << "Yes" << endl
#define cN cout << "No" << endl
const long long INF = 1LL << 60;
long long MOD = 1000000007;
const long double pi = 3.1415926535897932;
#define pb push_back
#define mp make_pair
#define mt make_tuple
using Grid = vector<vector<char>>;
#define vc vector<char>
//(mod m)でのaの逆元を計算する
// a/b(mod m)=a(mod m)*modinv(b,m)
long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

// 最大最小の入れ替え
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;
}

// 約数列挙
vector<long long> divisor(long long n) {
  vector<long long> ret;
  for (long long i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end()); // 昇順に並べる
  return ret;
}
// コンビネーション
ll nCr(ll n, ll r) {
  ll ans = 1;
  for (ll i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (ll i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}
// 素因数分解
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

// 切り上げの割り算は(a + b - 1) / bでできる

// ここから
int main() {
  ll H, W, K;
  cin >> H >> W >> K;
  Grid G(W, vc(H));
  ll sx, sy;
  rep(i, H) {
    rep(j, W) {
      cin >> G[j][i];
      if (G[j][i] == 'S') {
        sx = j;
        sy = i;
      }
    }
  }
  ll dist = INF;
  vector<vector<bool>> visit(W, vector<bool>(H, false));
  queue<pll> q;
  pll w = mp(sx, sy);
  q.push(w);
  map<pll, ll> D;
  D[w] = 0;
  ll dx[4] = {1, 0, -1, 0};
  ll dy[4] = {0, 1, 0, -1};
  visit[sx][sy] = true;
  while (!q.empty()) {
    pll P = q.front();
    q.pop();
    ll x = P.first;
    ll y = P.second;
    dist = min({dist, x, W - x - 1, y, H - y - 1});
    visit[x][y] = true;
    if (D[P] == K)
      continue;
    rep(i, 4) {
      ll nx = x + dx[i];
      ll ny = y + dy[i];
      if (nx < 0 || ny < 0 || ny > H - 1 || nx > W - 1 || visit[nx][ny])
        continue;
      if (G[nx][ny] == '.') {
        if (nx == 0 || nx == W - 1 || ny == H - 1 || ny == 0) {
          cout << 1 << endl;
          return 0;
        } else {
          pll p = mp(nx, ny);
          q.push(p);
          D[p] = D[P] + 1;
          visit[nx][ny] = true;
        }
      }
    }
  }
  cout << 1 + (dist + K - 1) / K << endl;
}