Problem p02644 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define ll long long
#define IOS                                                                    \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define deb(x) cout << #x << "=" << x << endl;
#define endl '\n'
#define M 1000000007
#define int long long
#define INF 1e18
#define max_n 1000005

using namespace std;

ll h, w, k;
ll x1, yy1, x2, y2;
string a[max_n];
vector<vector<ll>> ans;
vector<vector<bool>> vis;
ll dx[] = {0, 0, 1, -1};
ll dy[] = {1, -1, 0, 0};

void bfs(ll x, ll y) {
  ans[x][y] = 0;
  vis[x][y] = true;
  queue<pair<ll, ll>> q;
  q.push({x, y});
  while (!q.empty()) {
    ll xx = q.front().first, yy = q.front().second;
    // cout<<xx<<" "<<yy<<endl;
    q.pop();
    for (int j = 0; j < 4; ++j) {
      for (int i = 1; i <= k; ++i) {
        ll nx = xx + dx[j] * i;
        ll ny = yy + dy[j] * i;
        if (nx < 0 || ny < 0 || nx >= h || ny >= w || a[nx][ny] == '@')
          break;
        if (vis[nx][ny])
          continue;
        vis[nx][ny] = true;
        ans[nx][ny] = ans[xx][yy] + 1;
        // deb(ans[nx][ny])
        q.push({nx, ny});
      }
    }
  }
}

void solve() {
  cin >> h >> w >> k;
  cin >> x1 >> yy1 >> x2 >> y2;
  for (int i = 0; i < h; ++i) {
    cin >> a[i];
  }
  x1--;
  yy1--;
  x2--;
  y2--;
  ans = vector<vector<ll>>(h, vector<ll>(w, -1LL));
  vis = vector<vector<bool>>(h, vector<bool>(w, false));
  bfs(x1, yy1);
  cout << ans[x2][y2] << endl;
}

int32_t main() {
  IOS ll T = 1;
  // cin>>T;
  for (ll i = 1; i <= T; ++i) {
    // cout<<"Case #"<<i<<": ";
    solve();
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define ll long long
#define IOS                                                                    \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define deb(x) cout << #x << "=" << x << endl;
#define endl '\n'
#define M 1000000007
#define int long long
#define INF 1e18
#define max_n 1000005

using namespace std;

ll h, w, k;
ll x1, yy1, x2, y2;
string a[max_n];
vector<vector<ll>> ans;
vector<vector<bool>> vis;
ll dx[] = {0, 0, 1, -1};
ll dy[] = {1, -1, 0, 0};

void bfs(ll x, ll y) {
  ans[x][y] = 0;
  vis[x][y] = true;
  queue<pair<ll, ll>> q;
  q.push({x, y});
  while (!q.empty()) {
    ll xx = q.front().first, yy = q.front().second;
    // cout<<xx<<" "<<yy<<endl;
    q.pop();
    for (int j = 0; j < 4; ++j) {
      for (int i = 1; i <= k; ++i) {
        ll nx = xx + dx[j] * i;
        ll ny = yy + dy[j] * i;
        if (nx < 0 || ny < 0 || nx >= h || ny >= w || a[nx][ny] == '@')
          break;
        if (vis[nx][ny] && ans[nx][ny] < ans[xx][yy] + 1LL)
          break;
        if (vis[nx][ny])
          continue;
        vis[nx][ny] = true;
        ans[nx][ny] = ans[xx][yy] + 1;
        // deb(ans[nx][ny])
        q.push({nx, ny});
      }
    }
  }
}

void solve() {
  cin >> h >> w >> k;
  cin >> x1 >> yy1 >> x2 >> y2;
  for (int i = 0; i < h; ++i) {
    cin >> a[i];
  }
  x1--;
  yy1--;
  x2--;
  y2--;
  ans = vector<vector<ll>>(h, vector<ll>(w, -1LL));
  vis = vector<vector<bool>>(h, vector<bool>(w, false));
  bfs(x1, yy1);
  cout << ans[x2][y2] << endl;
}

int32_t main() {
  IOS ll T = 1;
  // cin>>T;
  for (ll i = 1; i <= T; ++i) {
    // cout<<"Case #"<<i<<": ";
    solve();
  }
  return 0;
}