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

#include <bits/stdc++.h>
#define ll long long
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define repi(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
#define repm(i, a, b) for (ll i = (ll)(a); i > (ll)(b); i--)
#define all(v) v.begin(), v.end()
#define rall(x) (x).rbegin(), (x).rend()
#define pll pair<long long, long long>
#define pb emplace_back
#define mp make_pair
#define mt make_tuple
#define vc vector<char>
#define vvc vector<vc>
using namespace std;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<long long>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vvb = vector<vb>;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
// snippets:tmp,cl,cvl,cs,co,coy,con,cov,setp

int main() {
  int h;
  cin >> h;
  int w;
  cin >> w;
  int ch;
  cin >> ch;
  int cw;
  cin >> cw;
  int dh;
  cin >> dh;
  int dw;
  cin >> dw;
  vvi s(h, vi(w));
  rep(i, h) {
    string st;
    cin >> st;
    rep(j, w) {
      if (st[j] == '.')
        s[i][j] = 1;
      else
        s[i][j] = 0;
    }
  }
  vvi d(h, vi(w, -1));
  queue<pair<int, int>> q;
  queue<pair<int, int>> q2;
  vvi check(h, vi(w, 0));
  q.push({ch - 1, cw - 1});
  q2.push({ch - 1, cw - 1});
  d[ch - 1][cw - 1] = 0;
  while (!q.empty() || !q2.empty()) {
    while (!q.empty()) {
      ll x = q.front().first;
      ll y = q.front().second;
      q2.push({x, y});
      if (x != 0) {
        if (s[x - 1][y]) {
          if (d[x - 1][y] == -1 || d[x][y] < d[x - 1][y]) {
            d[x - 1][y] = d[x][y];
            if (!check[x - 1][y]) {
              q.push({x - 1, y});
              q2.push({x - 1, y});
            }
            check[x - 1][y] = 1;
          }
        }
      }
      if (y != 0) {
        if (s[x][y - 1]) {
          if (d[x][y - 1] == -1 || d[x][y] < d[x][y - 1]) {
            d[x][y - 1] = d[x][y];
            if (!check[x][y - 1]) {
              q.push({x, y - 1});
              q2.push({x, y - 1});
            }
            check[x][y - 1] = 1;
          }
        }
      }
      if (x != h - 1) {
        if (s[x + 1][y]) {
          if (d[x + 1][y] == -1 || d[x][y] < d[x + 1][y]) {
            d[x + 1][y] = d[x][y];
            if (!check[x + 1][y]) {
              q.push({x + 1, y});
              q2.push({x + 1, y});
            }
            check[x + 1][y] = 1;
          }
        }
      }
      if (y != w - 1) {
        if (s[x][y + 1]) {
          if (d[x][y + 1] == -1 || d[x][y] < d[x][y + 1]) {
            d[x][y + 1] = d[x][y];
            if (!check[x][y + 1]) {
              q.push({x, y + 1});
              q2.push({x, y + 1});
            }
            check[x][y + 1] = 1;
          }
        }
      }
      q.pop();
      check[x][y] = 0;
    }

    if (d[dh - 1][dw - 1] != -1)
      break;
    while (!q2.empty()) {
      int x = q2.front().first;
      int y = q2.front().second;
      if (x != 0 && y != 0) {
        if (s[x - 1][y - 1]) {
          if (d[x - 1][y - 1] == -1 || d[x][y] + 1 < d[x - 1][y - 1]) {
            d[x - 1][y - 1] = d[x][y] + 1;
            if (!check[x - 1][y - 1])
              q.push({x - 1, y - 1});
            check[x - 1][y - 1] = 1;
          }
        }
      }
      if (x != h - 1 && y != w - 1) {
        if (s[x + 1][y + 1]) {
          if (d[x + 1][y + 1] == -1 || d[x][y] + 1 < d[x + 1][y + 1]) {
            d[x + 1][y + 1] = d[x][y] + 1;
            if (!check[x + 1][y + 1])
              q.push({x + 1, y + 1});
            check[x + 1][y + 1] = 1;
          }
        }
      }
      if (x != h - 1 && y != 0) {
        if (s[x + 1][y - 1]) {
          if (d[x + 1][y - 1] == -1 || d[x][y] + 1 < d[x + 1][y - 1]) {
            d[x + 1][y - 1] = d[x][y] + 1;
            if (!check[x + 1][y - 1])
              q.push({x + 1, y - 1});
            check[x + 1][y - 1] = 1;
          }
        }
      }
      if (x != 0 && y != w - 1) {
        if (s[x - 1][y + 1]) {
          if (d[x - 1][y + 1] == -1 || d[x][y] + 1 < d[x - 1][y + 1]) {
            d[x - 1][y + 1] = d[x][y] + 1;
            if (!check[x - 1][y + 1])
              q.push({x - 1, y + 1});
            check[x - 1][y + 1] = 1;
          }
        }
      }
      if (x > 1 && y > 1) {
        if (s[x - 2][y - 2]) {
          if (d[x - 2][y - 2] == -1 || d[x][y] + 1 < d[x - 2][y - 2]) {
            d[x - 2][y - 2] = d[x][y] + 1;
            if (!check[x - 2][y - 2])
              q.push({x - 2, y - 2});
            check[x - 2][y - 2] = 1;
          }
        }
      }
      if (x > 0 && y > 1) {
        if (s[x - 1][y - 2]) {
          if (d[x - 1][y - 2] == -1 || d[x][y] + 1 < d[x - 1][y - 2]) {
            d[x - 1][y - 2] = d[x][y] + 1;
            if (!check[x - 1][y - 2])
              q.push({x - 1, y - 2});
            check[x - 1][y - 2] = 1;
          }
        }
      }
      if (y > 1) {
        if (s[x][y - 2]) {
          if (d[x][y - 2] == -1 || d[x][y] + 1 < d[x][y - 2]) {
            d[x][y - 2] = d[x][y] + 1;
            if (!check[x][y - 2])
              q.push({x, y - 2});
            check[x][y - 2] = 1;
          }
        }
      }
      if (x < h - 1 && y > 1) {
        if (s[x + 1][y - 2]) {
          if (d[x + 1][y - 2] == -1 || d[x][y] + 1 < d[x + 1][y - 2]) {
            d[x + 1][y - 2] = d[x][y] + 1;
            if (!check[x + 1][y - 2])
              q.push({x + 1, y - 2});
            check[x + 1][y - 2] = 1;
          }
        }
      }
      if (x < (h - 2) && y > 1) {
        if (s[x + 2][y - 2]) {
          if (d[x + 2][y - 2] == -1 || d[x][y] + 1 < d[x + 2][y - 2]) {
            d[x + 2][y - 2] = d[x][y] + 1;
            if (!check[x + 2][y - 2])
              q.push({x + 2, y - 2});
            check[x + 2][y - 2] = 1;
          }
        }
      }
      if (x < (h - 2) && y > 0) {
        if (s[x + 2][y - 1]) {
          if (d[x + 2][y - 1] == -1 || d[x][y] + 1 < d[x + 2][y - 1]) {
            d[x + 2][y - 1] = d[x][y] + 1;
            if (!check[x + 2][y - 1])
              q.push({x + 2, y - 1});
            check[x + 2][y - 1] = 1;
          }
        }
      }
      if (x < (h - 2)) {
        if (s[x + 2][y]) {
          if (d[x + 2][y] == -1 || d[x][y] + 1 < d[x + 2][y]) {
            d[x + 2][y] = d[x][y] + 1;
            if (!check[x + 2][y])
              q.push({x + 2, y});
            check[x + 2][y] = 1;
          }
        }
      }
      if (x < (h - 2) && y < w - 1) {
        if (s[x + 2][y + 1]) {
          if (d[x + 2][y + 1] == -1 || d[x][y] + 1 < d[x + 2][y + 1]) {
            d[x + 2][y + 1] = d[x][y] + 1;
            if (!check[x + 2][y + 1])
              q.push({x + 2, y + 1});
            check[x + 2][y + 1] = 1;
          }
        }
      }
      if (x < (h - 2) && y < (w - 2)) {
        if (s[x + 2][y + 2]) {
          if (d[x + 2][y + 2] == -1 || d[x][y] + 1 < d[x + 2][y + 2]) {
            d[x + 2][y + 2] = d[x][y] + 1;
            if (!check[x + 2][y + 2])
              q.push({x + 2, y + 2});
            check[x + 2][y + 2] = 1;
          }
        }
      }
      if (x < h - 1 && y < (w - 2)) {
        if (s[x + 1][y + 2]) {
          if (d[x + 1][y + 2] == -1 || d[x][y] + 1 < d[x + 1][y + 2]) {
            d[x + 1][y + 2] = d[x][y] + 1;
            if (!check[x + 1][y + 2])
              q.push({x + 1, y + 2});
            check[x + 1][y + 2] = 1;
          }
        }
      }
      if (y < (w - 2)) {
        if (s[x][y + 2]) {
          if (d[x][y + 2] == -1 || d[x][y] + 1 < d[x][y + 2]) {
            d[x][y + 2] = d[x][y] + 1;
            if (!check[x][y + 2])
              q.push({x, y + 2});
            check[x][y + 2] = 1;
          }
        }
      }
      if (x > 0 && y < (w - 2)) {
        if (s[x - 1][y + 2]) {
          if (d[x - 1][y + 2] == -1 || d[x][y] + 1 < d[x - 1][y + 2]) {
            d[x - 1][y + 2] = d[x][y] + 1;
            if (!check[x - 1][y + 2])
              q.push({x - 1, y + 2});
            check[x - 1][y + 2] = 1;
          }
        }
      }
      if (x > 1 && y < (w - 2)) {
        if (s[x - 2][y + 2]) {
          if (d[x - 2][y + 2] == -1 || d[x][y] + 1 < d[x - 2][y + 2]) {
            d[x - 2][y + 2] = d[x][y] + 1;
            if (!check[x - 2][y + 2])
              q.push({x - 2, y + 2});
            check[x - 2][y + 2] = 1;
          }
        }
      }
      if (x > 1 && y < w - 1) {
        if (s[x - 2][y + 1]) {
          if (d[x - 2][y + 1] == -1 || d[x][y] + 1 < d[x - 2][y + 1]) {
            d[x - 2][y + 1] = d[x][y] + 1;
            if (!check[x - 2][y + 1])
              q.push({x - 2, y + 1});
            check[x - 2][y + 1] = 1;
          }
        }
      }
      if (x > 1 && y) {
        if (s[x - 2][y]) {
          if (d[x - 2][y] == -1 || d[x][y] + 1 < d[x - 2][y]) {
            d[x - 2][y] = d[x][y] + 1;
            if (!check[x - 2][y])
              q.push({x - 2, y});
            check[x - 2][y] = 1;
          }
        }
      }
      if (x > 1 && y > 0) {
        if (s[x - 2][y - 1]) {
          if (d[x - 2][y - 1] == -1 || d[x][y] + 1 < d[x - 2][y - 1]) {
            d[x - 2][y - 1] = d[x][y] + 1;
            if (!check[x - 2][y - 1])
              q.push({x - 2, y - 1});
            check[x - 2][y - 1] = 1;
          }
        }
      }
      q2.pop();
      check[x][y] = 0;
    }
  }
  cout << d[dh - 1][dw - 1] << endl;
}


Error: TLE

Fixed submission:

#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#define ll long long
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define repi(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
#define repm(i, a, b) for (ll i = (ll)(a); i > (ll)(b); i--)
#define all(v) v.begin(), v.end()
#define rall(x) (x).rbegin(), (x).rend()
#define pll pair<long long, long long>
#define pb emplace_back
#define mp make_pair
#define mt make_tuple
#define vc vector<char>
#define vvc vector<vc>
using namespace std;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<long long>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vvb = vector<vb>;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
// snippets:tmp,cl,cvl,cs,co,coy,con,cov,setp

int main() {
  int h;
  cin >> h;
  int w;
  cin >> w;
  int ch;
  cin >> ch;
  int cw;
  cin >> cw;
  int dh;
  cin >> dh;
  int dw;
  cin >> dw;
  vvi s(h, vi(w));
  rep(i, h) {
    string st;
    cin >> st;
    rep(j, w) {
      if (st[j] == '.')
        s[i][j] = 1;
      else
        s[i][j] = 0;
    }
  }
  vvi d(h, vi(w, -1));
  queue<pair<int, int>> q;
  vvi check(h, vi(w, 0));
  q.push({ch - 1, cw - 1});
  d[ch - 1][cw - 1] = 0;
  while (!q.empty()) {
    ll x = q.front().first;
    ll y = q.front().second;
    if (x != 0) {
      if (s[x - 1][y]) {
        if (d[x - 1][y] == -1 || d[x][y] < d[x - 1][y]) {
          d[x - 1][y] = d[x][y];
          if (!check[x - 1][y])
            q.push({x - 1, y});
          check[x - 1][y] = 1;
        }
      }
    }
    if (y != 0) {
      if (s[x][y - 1]) {
        if (d[x][y - 1] == -1 || d[x][y] < d[x][y - 1]) {
          d[x][y - 1] = d[x][y];
          if (!check[x][y - 1])
            q.push({x, y - 1});
          check[x][y - 1] = 1;
        }
      }
    }
    if (x != h - 1) {
      if (s[x + 1][y]) {
        if (d[x + 1][y] == -1 || d[x][y] < d[x + 1][y]) {
          d[x + 1][y] = d[x][y];
          if (!check[x + 1][y])
            q.push({x + 1, y});
          check[x + 1][y] = 1;
        }
      }
    }
    if (y != w - 1) {
      if (s[x][y + 1]) {
        if (d[x][y + 1] == -1 || d[x][y] < d[x][y + 1]) {
          d[x][y + 1] = d[x][y];
          if (!check[x][y + 1])
            q.push({x, y + 1});
          check[x][y + 1] = 1;
        }
      }
    }
    if (x != 0 && y != 0) {
      if (s[x - 1][y - 1]) {
        if (d[x - 1][y - 1] == -1 || d[x][y] + 1 < d[x - 1][y - 1]) {
          d[x - 1][y - 1] = d[x][y] + 1;
          if (!check[x - 1][y - 1])
            q.push({x - 1, y - 1});
          check[x - 1][y - 1] = 1;
        }
      }
    }
    if (x != h - 1 && y != w - 1) {
      if (s[x + 1][y + 1]) {
        if (d[x + 1][y + 1] == -1 || d[x][y] + 1 < d[x + 1][y + 1]) {
          d[x + 1][y + 1] = d[x][y] + 1;
          if (!check[x + 1][y + 1])
            q.push({x + 1, y + 1});
          check[x + 1][y + 1] = 1;
        }
      }
    }
    if (x != h - 1 && y != 0) {
      if (s[x + 1][y - 1]) {
        if (d[x + 1][y - 1] == -1 || d[x][y] + 1 < d[x + 1][y - 1]) {
          d[x + 1][y - 1] = d[x][y] + 1;
          if (!check[x + 1][y - 1])
            q.push({x + 1, y - 1});
          check[x + 1][y - 1] = 1;
        }
      }
    }
    if (x != 0 && y != w - 1) {
      if (s[x - 1][y + 1]) {
        if (d[x - 1][y + 1] == -1 || d[x][y] + 1 < d[x - 1][y + 1]) {
          d[x - 1][y + 1] = d[x][y] + 1;
          if (!check[x - 1][y + 1])
            q.push({x - 1, y + 1});
          check[x - 1][y + 1] = 1;
        }
      }
    }
    if (x > 1 && y > 1) {
      if (s[x - 2][y - 2]) {
        if (d[x - 2][y - 2] == -1 || d[x][y] + 1 < d[x - 2][y - 2]) {
          d[x - 2][y - 2] = d[x][y] + 1;
          if (!check[x - 2][y - 2])
            q.push({x - 2, y - 2});
          check[x - 2][y - 2] = 1;
        }
      }
    }
    if (x > 0 && y > 1) {
      if (s[x - 1][y - 2]) {
        if (d[x - 1][y - 2] == -1 || d[x][y] + 1 < d[x - 1][y - 2]) {
          d[x - 1][y - 2] = d[x][y] + 1;
          if (!check[x - 1][y - 2])
            q.push({x - 1, y - 2});
          check[x - 1][y - 2] = 1;
        }
      }
    }
    if (y > 1) {
      if (s[x][y - 2]) {
        if (d[x][y - 2] == -1 || d[x][y] + 1 < d[x][y - 2]) {
          d[x][y - 2] = d[x][y] + 1;
          if (!check[x][y - 2])
            q.push({x, y - 2});
          check[x][y - 2] = 1;
        }
      }
    }
    if (x < h - 1 && y > 1) {
      if (s[x + 1][y - 2]) {
        if (d[x + 1][y - 2] == -1 || d[x][y] + 1 < d[x + 1][y - 2]) {
          d[x + 1][y - 2] = d[x][y] + 1;
          if (!check[x + 1][y - 2])
            q.push({x + 1, y - 2});
          check[x + 1][y - 2] = 1;
        }
      }
    }
    if (x < (h - 2) && y > 1) {
      if (s[x + 2][y - 2]) {
        if (d[x + 2][y - 2] == -1 || d[x][y] + 1 < d[x + 2][y - 2]) {
          d[x + 2][y - 2] = d[x][y] + 1;
          if (!check[x + 2][y - 2])
            q.push({x + 2, y - 2});
          check[x + 2][y - 2] = 1;
        }
      }
    }
    if (x < (h - 2) && y > 0) {
      if (s[x + 2][y - 1]) {
        if (d[x + 2][y - 1] == -1 || d[x][y] + 1 < d[x + 2][y - 1]) {
          d[x + 2][y - 1] = d[x][y] + 1;
          if (!check[x + 2][y - 1])
            q.push({x + 2, y - 1});
          check[x + 2][y - 1] = 1;
        }
      }
    }
    if (x < (h - 2)) {
      if (s[x + 2][y]) {
        if (d[x + 2][y] == -1 || d[x][y] + 1 < d[x + 2][y]) {
          d[x + 2][y] = d[x][y] + 1;
          if (!check[x + 2][y])
            q.push({x + 2, y});
          check[x + 2][y] = 1;
        }
      }
    }
    if (x < (h - 2) && y < w - 1) {
      if (s[x + 2][y + 1]) {
        if (d[x + 2][y + 1] == -1 || d[x][y] + 1 < d[x + 2][y + 1]) {
          d[x + 2][y + 1] = d[x][y] + 1;
          if (!check[x + 2][y + 1])
            q.push({x + 2, y + 1});
          check[x + 2][y + 1] = 1;
        }
      }
    }
    if (x < (h - 2) && y < (w - 2)) {
      if (s[x + 2][y + 2]) {
        if (d[x + 2][y + 2] == -1 || d[x][y] + 1 < d[x + 2][y + 2]) {
          d[x + 2][y + 2] = d[x][y] + 1;
          if (!check[x + 2][y + 2])
            q.push({x + 2, y + 2});
          check[x + 2][y + 2] = 1;
        }
      }
    }
    if (x < h - 1 && y < (w - 2)) {
      if (s[x + 1][y + 2]) {
        if (d[x + 1][y + 2] == -1 || d[x][y] + 1 < d[x + 1][y + 2]) {
          d[x + 1][y + 2] = d[x][y] + 1;
          if (!check[x + 1][y + 2])
            q.push({x + 1, y + 2});
          check[x + 1][y + 2] = 1;
        }
      }
    }
    if (y < (w - 2)) {
      if (s[x][y + 2]) {
        if (d[x][y + 2] == -1 || d[x][y] + 1 < d[x][y + 2]) {
          d[x][y + 2] = d[x][y] + 1;
          if (!check[x][y + 2])
            q.push({x, y + 2});
          check[x][y + 2] = 1;
        }
      }
    }
    if (x > 0 && y < (w - 2)) {
      if (s[x - 1][y + 2]) {
        if (d[x - 1][y + 2] == -1 || d[x][y] + 1 < d[x - 1][y + 2]) {
          d[x - 1][y + 2] = d[x][y] + 1;
          if (!check[x - 1][y + 2])
            q.push({x - 1, y + 2});
          check[x - 1][y + 2] = 1;
        }
      }
    }
    if (x > 1 && y < (w - 2)) {
      if (s[x - 2][y + 2]) {
        if (d[x - 2][y + 2] == -1 || d[x][y] + 1 < d[x - 2][y + 2]) {
          d[x - 2][y + 2] = d[x][y] + 1;
          if (!check[x - 2][y + 2])
            q.push({x - 2, y + 2});
          check[x - 2][y + 2] = 1;
        }
      }
    }
    if (x > 1 && y < w - 1) {
      if (s[x - 2][y + 1]) {
        if (d[x - 2][y + 1] == -1 || d[x][y] + 1 < d[x - 2][y + 1]) {
          d[x - 2][y + 1] = d[x][y] + 1;
          if (!check[x - 2][y + 1])
            q.push({x - 2, y + 1});
          check[x - 2][y + 1] = 1;
        }
      }
    }
    if (x > 1 && y) {
      if (s[x - 2][y]) {
        if (d[x - 2][y] == -1 || d[x][y] + 1 < d[x - 2][y]) {
          d[x - 2][y] = d[x][y] + 1;
          if (!check[x - 2][y])
            q.push({x - 2, y});
          check[x - 2][y] = 1;
        }
      }
    }
    if (x > 1 && y > 0) {
      if (s[x - 2][y - 1]) {
        if (d[x - 2][y - 1] == -1 || d[x][y] + 1 < d[x - 2][y - 1]) {
          d[x - 2][y - 1] = d[x][y] + 1;
          if (!check[x - 2][y - 1])
            q.push({x - 2, y - 1});
          check[x - 2][y - 1] = 1;
        }
      }
    }
    q.pop();
    check[x][y] = 0;
  }
  cout << d[dh - 1][dw - 1] << endl;
}