Problem p02579 (C++) — buggy submission, verdict: Time Limit Exceeded

#pragma GCC optimize("O3")
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <istream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
#define IINF 1000000000
#define INF 3223372036854775807
#define MOD 1000000007
#define mod 1000000007
#define INT_MAX_ 2147483647
#define EPS (1e-10)
#define REP(i, a, n) fo - r(ll i = a; i < (ll)(n); i++)
#define REPE(i, a, n) for (ll i = a; i <= (ll)(n); i++)
// #define rep(i,n)for (ll i = 0; i < (ll)(n); i++)
#define rep(i, l, r) for (ll i = (l); i < (r); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define Endl endl
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define eb emplace_back
#define mmax(x, y) (x > y ? x : y)
#define mmin(x, y) (x < y ? x : y)
#define chmax(x, y) x = mmax(x, y)
#define chmin(x, y) x = mmin(x, y)
#define all(x) (x).begin(), (x).end()
#define siz(x) (ll)(x).size()
#define PI acos(-1.0)
#define me memset
#define bit(n, k) ((n >> k) & 1)
#define lg length()
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;
typedef long double ld;
typedef pair<int, int> Pin;
typedef pair<ll, ll> Pll;
template <class T> using V = vector<T>;
template <typename T>
using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
long long GCD(long long a, long long b) { return b ? GCD(b, a % b) : a; }
long long LCM(long long a, long long b) { return a / GCD(a, b) * b; }
ll pom(ll a, ll n, int m) {
  ll x = 1;
  for (a %= m; n; n /= 2)
    n & 1 ? x = x * a % m : 0, a = a * a % m;
  return x;
}
#define invp(a, p) pom(a, p - 2, p)
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};
int ddx[8] = {-1, 0, 1, 0, 1, 1, -1, -1};
int ddy[8] = {0, -1, 0, 1, 1, -1, 1, -1};
ll cmp1(pair<Pll, ll> a, pair<Pll, ll> b) { return a.fi.se > b.fi.se; }
ll cmp2(pair<ll, ll> a, pair<ll, ll> b) {
  if (a.se != b.se)
    return a.se < b.se;
  else
    return a.fi < b.fi;
}
//----------------------------------------------------------------------
ll num[1001][1001];
bool ccolor[1000001];
V<Pll> cal[1000001];
ll magic[1000001];
//----------------------------------------------------------------------
int main(int argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  //-------------------------------
  // ll begin_t=clock();
  // freopen("big.txt", "r", stdin);
  // freopen("out3.txt", "w", stdout);
  //------------------------------
  ll h, w;
  cin >> h >> w;
  char s[1001][1001];
  ll ch, cw, dh, dw;
  cin >> ch >> cw >> dh >> dw;
  ch--;
  cw--;
  dh--;
  dw--;
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++) {
      cin >> s[i][j];
    }
  }
  ll now = 1;
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++) {
      if (s[i][j] == '.' && num[i][j] == 0) {
        num[i][j] = now;
        queue<Pll> q;
        q.push(mp(i, j));
        while (!q.empty()) {
          Pll p = q.front();
          q.pop();
          ll x = p.fi, y = p.se;
          for (ll i = 0; i < 4; i++) {
            ll nx = x + dx[i];
            ll ny = y + dy[i];
            if (nx >= 0 && nx < h && ny >= 0 && ny < w) {
              if (s[nx][ny] == '#')
                continue;
              if (num[nx][ny])
                continue;
              num[nx][ny] = now;
              q.push(mp(nx, ny));
            }
          }
        }
        now++;
      }
    }
  }
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++) {
      if (s[i][j] == '.') {
        cal[num[i][j]].pb({i, j});
      }
    }
  }
  for (ll i = 0; i <= 1000000; i++)
    magic[i] = INF;

  now = num[ch][cw];
  queue<ll> C;
  C.push(now);
  magic[now] = 0;
  while (!C.empty()) {
    bool abc = 0;
    ll t = C.front();
    C.pop();
    for (ll i = 0; i < cal[t].size(); i++) {
      ll x = cal[t][i].fi;
      ll y = cal[t][i].se;
      if (x == dh && y == dw) {
        abc = 1;
        break;
      }
      for (ll nx = x - 2; nx <= x + 2; nx++) {
        for (ll ny = y - 2; ny <= y + 2; ny++) {
          if (nx >= 0 && nx < h && ny >= 0 && ny < w) {
            if (s[nx][ny] == '#')
              continue;
            if (num[nx][ny] == num[x][y])
              continue;
            if (magic[num[nx][ny]] == INF) {
              chmin(magic[num[nx][ny]], magic[num[x][y]] + 1);
              C.push(num[nx][ny]);
            }
          }
        }
      }
    }
    if (abc == 1)
      break;
  }
  if (magic[num[dh][dw]] == INF)
    cout << -1 << endl;
  else
    cout << magic[num[dh][dw]] << Endl;
  //------------------------------
  // fclose(stdin);
  // fclose(stdout);
  // ll end_t=clock();cout<<"time="<<end_t-begin_t<<"ms"<<endl;
  //-------------------------------
  return 0;
}
//----------------------------------------------------------------------


Error: TLE

Fixed submission:

#pragma GCC optimize("O3")
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <istream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
#define IINF 1000000000
#define INF 3223372036854775807
#define MOD 1000000007
#define mod 1000000007
#define INT_MAX_ 2147483647
#define EPS (1e-10)
#define REP(i, a, n) fo - r(ll i = a; i < (ll)(n); i++)
#define REPE(i, a, n) for (ll i = a; i <= (ll)(n); i++)
// #define rep(i,n)for (ll i = 0; i < (ll)(n); i++)
#define rep(i, l, r) for (ll i = (l); i < (r); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define Endl endl
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define eb emplace_back
#define mmax(x, y) (x > y ? x : y)
#define mmin(x, y) (x < y ? x : y)
#define chmax(x, y) x = mmax(x, y)
#define chmin(x, y) x = mmin(x, y)
#define all(x) (x).begin(), (x).end()
#define siz(x) (ll)(x).size()
#define PI acos(-1.0)
#define me memset
#define bit(n, k) ((n >> k) & 1)
#define lg length()
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;
typedef long double ld;
typedef pair<int, int> Pin;
typedef pair<ll, ll> Pll;
template <class T> using V = vector<T>;
template <typename T>
using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
long long GCD(long long a, long long b) { return b ? GCD(b, a % b) : a; }
long long LCM(long long a, long long b) { return a / GCD(a, b) * b; }
ll pom(ll a, ll n, int m) {
  ll x = 1;
  for (a %= m; n; n /= 2)
    n & 1 ? x = x * a % m : 0, a = a * a % m;
  return x;
}
#define invp(a, p) pom(a, p - 2, p)
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};
int ddx[8] = {-1, 0, 1, 0, 1, 1, -1, -1};
int ddy[8] = {0, -1, 0, 1, 1, -1, 1, -1};
ll cmp1(pair<Pll, ll> a, pair<Pll, ll> b) { return a.fi.se > b.fi.se; }
ll cmp2(pair<ll, ll> a, pair<ll, ll> b) {
  if (a.se != b.se)
    return a.se < b.se;
  else
    return a.fi < b.fi;
}
//----------------------------------------------------------------------
ll magic[1001][1001];

ll num[1001][1001];
bool color[1001][1001];
ll min_num[1000100];
//----------------------------------------------------------------------
int main(int argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  //-------------------------------
  // ll begin_t=clock();
  // freopen("big.txt", "r", stdin);
  // freopen("out3.txt", "w", stdout);
  //------------------------------
  ll h, w;
  cin >> h >> w;
  char s[1001][1001];
  ll ch, cw, dh, dw;
  cin >> ch >> cw >> dh >> dw;
  ch--;
  cw--;
  dh--;
  dw--;
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++) {
      cin >> s[i][j];
      magic[i][j] = INF;
    }
  }
  for (ll i = 0; i <= 1000000; i++) {
    min_num[i] = INF;
  }
  ll now = 1;
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++) {
      if (s[i][j] == '.' && color[i][j] == 0) {
        color[i][j] = 1;
        num[i][j] = now;
        queue<Pll> q;
        q.push(mp(i, j));
        while (!q.empty()) {
          Pll p = q.front();
          q.pop();
          ll x = p.fi, y = p.se;
          for (ll i = 0; i < 4; i++) {
            ll nx = x + dx[i];
            ll ny = y + dy[i];
            if (nx >= 0 && nx < h && ny >= 0 && ny < w) {
              if (s[nx][ny] == '#')
                continue;
              if (color[nx][ny])
                continue;
              color[nx][ny] = 1;
              num[nx][ny] = now;
              q.push(mp(nx, ny));
            }
          }
        }
        now++;
      }
    }
  }

  queue<Pll> Q;
  Q.push(mp(ch, cw));
  magic[ch][cw] = 0;
  min_num[num[ch][cw]] = 0;
  while (!Q.empty()) {
    Pll now = Q.front();
    Q.pop();
    ll x = now.fi, y = now.se;
    for (ll i = 0; i < 4; i++) {
      ll nx = x + dx[i];
      ll ny = y + dy[i];
      if (nx >= 0 && nx < h && ny >= 0 && ny < w) {
        if (s[nx][ny] == '#')
          continue;
        if (magic[nx][ny] <= magic[x][y])
          continue;
        chmin(magic[nx][ny], magic[x][y]);
        Q.push(mp(nx, ny));
      }
    }
    for (ll nx = x - 2; nx <= x + 2; nx++) {
      for (ll ny = y - 2; ny <= y + 2; ny++) {
        if (nx >= 0 && nx < h && ny >= 0 && ny < w) {
          if (s[nx][ny] == '#')
            continue;
          if (num[nx][ny] == num[x][y])
            continue;
          if (magic[nx][ny] <= magic[x][y] + 1)
            continue;
          if (min_num[num[nx][ny]] <= magic[x][y] + 1)
            continue;
          chmin(min_num[num[nx][ny]], magic[x][y] + 1);
          chmin(magic[nx][ny], magic[x][y] + 1);
          Q.push(mp(nx, ny));
        }
      }
    }
  }

  if (magic[dh][dw] == INF)
    cout << -1 << Endl;
  else
    cout << magic[dh][dw] << Endl;
  //------------------------------
  // fclose(stdin);
  // fclose(stdout);
  // ll end_t=clock();cout<<"time="<<end_t-begin_t<<"ms"<<endl;
  //-------------------------------
  return 0;
}
//----------------------------------------------------------------------