Problem p03053 (C++)

Buggy submission (status: Time Limit Exceeded):
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize(3)
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC target("sse3","sse2","sse")
// #pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
// #pragma GCC target("f16c")
// #pragma GCC
// optimize("inline","fast-math","unroll-loops","no-stack-protector") #pragma
// GCC diagnostic error "-fwhole-program" #pragma GCC diagnostic error
// "-fcse-skip-blocks" #pragma GCC diagnostic error
// "-funsafe-loop-optimizations" #pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
// #include "ext/pb_ds/tree_policy.hpp"
// #include "ext/pb_ds/assoc_container.hpp"
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (ll x = l; x < u; x++)
#define RREP(x, l, u) for (ll x = l; x >= u; x--)
#define complete_unique(a) a.erase(unique(a.begin(), a.end()), a.end())
#define mst(x, a) memset(x, a, sizeof(x))
#define all(a) a.begin(), a.end()
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define sqr(x) ((x) * (x))
#define lowbit(x) ((x) & (-(x)))
#define lson (ind << 1)
#define rson (ind << 1 | 1)
#define se second
#define fi first
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const ld eps = 1e-9;
const db PI = atan(1) * 4;
template <typename T> inline int sign(const T &a) {
  if (a < 0)
    return -1;
  if (a > 0)
    return 1;
  return 0;
}
string to_string(string s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifndef ONLINE_JUDGE
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...)                                                               \
  {}
#endif

template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}

template <typename T> inline void in(T &x) {
  x = 0;
  T f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  x *= f;
}

ll twop(int x) { return 1LL << x; }

// m must be positive
template <typename T> T MOD(T a, T m) {
  a %= m;
  if (a < 0)
    a += m;
  return a;
}

// a must be relatively prime to m
template <typename T> T inverse(T a, T m) {
  a = MOD(a, m);
  if (a <= 1)
    return a;
  return MOD((1 - inverse(m, a) * m) / a, m);
}

template <typename A, typename B> inline void in(A &x, B &y) {
  in(x);
  in(y);
}
template <typename A, typename B, typename C> inline void in(A &x, B &y, C &z) {
  in(x);
  in(y);
  in(z);
}
template <typename A, typename B, typename C, typename D>
inline void in(A &x, B &y, C &z, D &d) {
  in(x);
  in(y);
  in(z);
  in(d);
}
ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }
namespace SOLVE {
char grid[1010][1010];
int n, m;
int dis[1010][1010];
void main() {
  in(n, m);
  mst(grid, '#');
  REP(i, 1, n + 1) scanf("%s", grid[i] + 1);
  queue<PII> q;
  REP(i, 1, n + 1) {
    REP(j, 1, m + 1) {
      dis[i][j] = inf;
      if (grid[i][j] == '#') {
        dis[i][j] = 0;
        q.push(MP(i, j));
      }
    }
  }
  int dx[] = {1, -1, 0, 0};
  int dy[] = {0, 0, 1, -1};
  while (sz(q)) {
    auto f = q.front();
    q.pop();
    REP(d, 0, 4) {
      int tx = dx[d] + f.fi, ty = dy[d] + f.se;
      if (dis[tx][ty] > dis[f.fi][f.se] + 1) {
        dis[tx][ty] = dis[f.fi][f.se] + 1;
        q.push(MP(tx, ty));
      }
    }
  }
  int ans = 0;
  REP(i, 1, n + 1) {
    REP(j, 1, m + 1) { upmax(ans, dis[i][j]); }
  }

  cout << ans << endl;
}
} // namespace SOLVE

signed main() {
#ifndef ONLINE_JUDGE
  fr("/Users/zhangqingchuan/Desktop/cp/cp/input.txt");
  fw("/Users/zhangqingchuan/Desktop/cp/cp/output.txt");
#endif

  int t = 1;
  //    in(t);
  while (t--) {
    SOLVE::main();
  }

  return 0;
}


Fixed submission:
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize(3)
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC target("sse3","sse2","sse")
// #pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
// #pragma GCC target("f16c")
// #pragma GCC
// optimize("inline","fast-math","unroll-loops","no-stack-protector") #pragma
// GCC diagnostic error "-fwhole-program" #pragma GCC diagnostic error
// "-fcse-skip-blocks" #pragma GCC diagnostic error
// "-funsafe-loop-optimizations" #pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
// #include "ext/pb_ds/tree_policy.hpp"
// #include "ext/pb_ds/assoc_container.hpp"
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (ll x = l; x < u; x++)
#define RREP(x, l, u) for (ll x = l; x >= u; x--)
#define complete_unique(a) a.erase(unique(a.begin(), a.end()), a.end())
#define mst(x, a) memset(x, a, sizeof(x))
#define all(a) a.begin(), a.end()
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define sqr(x) ((x) * (x))
#define lowbit(x) ((x) & (-(x)))
#define lson (ind << 1)
#define rson (ind << 1 | 1)
#define se second
#define fi first
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const ld eps = 1e-9;
const db PI = atan(1) * 4;
template <typename T> inline int sign(const T &a) {
  if (a < 0)
    return -1;
  if (a > 0)
    return 1;
  return 0;
}
string to_string(string s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifndef ONLINE_JUDGE
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...)                                                               \
  {}
#endif

template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}

template <typename T> inline void in(T &x) {
  x = 0;
  T f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  x *= f;
}

ll twop(int x) { return 1LL << x; }

// m must be positive
template <typename T> T MOD(T a, T m) {
  a %= m;
  if (a < 0)
    a += m;
  return a;
}

// a must be relatively prime to m
template <typename T> T inverse(T a, T m) {
  a = MOD(a, m);
  if (a <= 1)
    return a;
  return MOD((1 - inverse(m, a) * m) / a, m);
}

template <typename A, typename B> inline void in(A &x, B &y) {
  in(x);
  in(y);
}
template <typename A, typename B, typename C> inline void in(A &x, B &y, C &z) {
  in(x);
  in(y);
  in(z);
}
template <typename A, typename B, typename C, typename D>
inline void in(A &x, B &y, C &z, D &d) {
  in(x);
  in(y);
  in(z);
  in(d);
}
ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }
namespace SOLVE {
char grid[1010][1010];
int n, m;
int dis[1010][1010];
void main() {
  in(n, m);
  mst(grid, '#');
  REP(i, 1, n + 1) scanf("%s", grid[i] + 1);
  queue<PII> q;
  REP(i, 1, n + 1) {
    REP(j, 1, m + 1) {
      dis[i][j] = inf;
      if (grid[i][j] == '#') {
        dis[i][j] = 0;
        q.push(MP(i, j));
      }
    }
  }
  int dx[] = {1, -1, 0, 0};
  int dy[] = {0, 0, 1, -1};
  while (sz(q)) {
    auto f = q.front();
    q.pop();
    REP(d, 0, 4) {
      int tx = dx[d] + f.fi, ty = dy[d] + f.se;
      if (dis[tx][ty] > dis[f.fi][f.se] + 1) {
        dis[tx][ty] = dis[f.fi][f.se] + 1;
        q.push(MP(tx, ty));
      }
    }
  }
  int ans = 0;
  REP(i, 1, n + 1) {
    REP(j, 1, m + 1) { upmax(ans, dis[i][j]); }
  }

  cout << ans << endl;
}
} // namespace SOLVE

signed main() {

  int t = 1;
  //    in(t);
  while (t--) {
    SOLVE::main();
  }

  return 0;
}