Language: C++

#include <stdint.h>
#include <stdlib.h>

#include <algorithm>
#include <iostream>
#include <numeric>
#include <queue>
#include <vector>
using namespace std;
using default_counter_t = int64_t;

// macro
#define let auto const&
#define overload4(a, b, c, d, name, ...) name
#define rep1(n) \
  for (default_counter_t i = 0, end_i = default_counter_t(n); i < end_i; ++i)
#define rep2(i, n)                                                           \
  for (default_counter_t i = 0, end_##i = default_counter_t(n); i < end_##i; \
       ++i)
#define rep3(i, a, b)                                    \
  for (default_counter_t i       = default_counter_t(a), \
                         end_##i = default_counter_t(b); \
       i < end_##i; ++i)
#define rep4(i, a, b, c)                                 \
  for (default_counter_t i       = default_counter_t(a), \
                         end_##i = default_counter_t(b); \
       i < end_##i; i += default_counter_t(c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)

#define rrep1(n) \
  for (default_counter_t i = default_counter_t(n) - 1; i >= 0; --i)
#define rrep2(i, n) \
  for (default_counter_t i = default_counter_t(n) - 1; i >= 0; --i)
#define rrep3(i, a, b)                                         \
  for (default_counter_t i         = default_counter_t(b) - 1, \
                         begin_##i = default_counter_t(a);     \
       i >= begin_##i; --i)
#define rrep4(i, a, b, c)                                          \
  for (default_counter_t                                           \
           i = (default_counter_t(b) - default_counter_t(a) - 1) / \
                   default_counter_t(c) * default_counter_t(c) +   \
               default_counter_t(a),                               \
           begin_##i = default_counter_t(a);                       \
       i >= begin_##i; i -= default_counter_t(c))
#define rrep(...) \
  overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__)

#define ALL(f, c, ...)                                           \
  (([&](decltype((c)) cccc) {                                    \
    return (f)(std::begin(cccc), std::end(cccc), ##__VA_ARGS__); \
  })(c))

// function
template <class C>
constexpr C& Sort(C& a) {
  std::sort(std::begin(a), std::end(a));
  return a;
}
template <class C>
constexpr auto& Min(C const& a) {
  return *std::min_element(std::begin(a), std::end(a));
}
template <class C>
constexpr auto& Max(C const& a) {
  return *std::max_element(std::begin(a), std::end(a));
}
template <class C>
constexpr auto Total(C const& c) {
  return std::accumulate(std::begin(c), std::end(c), C(0));
}
template <typename T>
auto CumSum(std::vector<T> const& v) {
  std::vector<T> a(v.size() + 1, T(0));
  for (std::size_t i = 0; i < a.size() - size_t(1); ++i) a[i + 1] = a[i] + v[i];
  return a;
}
template <typename T>
constexpr bool ChMax(T& a, T const& b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
constexpr bool ChMin(T& a, T const& b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

void In(void) { return; }

template <typename First, typename... Rest>
void In(First& first, Rest&... rest) {
  cin >> first;
  In(rest...);
  return;
}

template <class T, typename I>
void VectorIn(vector<T>& v, const I n) {
  v.resize(size_t(n));
  rep(i, v.size()) cin >> v[i];
}

void Out(void) {
  cout << "\n";
  return;
}

template <typename First, typename... Rest>
void Out(First first, Rest... rest) {
  cout << first << " ";
  Out(rest...);
  return;
}

constexpr auto yes(const bool c) { return c ? "yes" : "no"; }
constexpr auto Yes(const bool c) { return c ? "Yes" : "No"; }
constexpr auto YES(const bool c) { return c ? "YES" : "NO"; }

// http://koturn.hatenablog.com/entry/2018/08/01/010000
template <typename T, typename U>
inline std::vector<U> MakeNdVector(T n, U val) noexcept {
  static_assert(std::is_integral<T>::value,
                "[MakeNdVector] The 1st argument must be an integer");
  return std::vector<U>(std::forward<T>(n), std::forward<U>(val));
}

template <typename T, typename... Args>
inline decltype(auto) MakeNdVector(T n, Args&&... args) noexcept {
  static_assert(std::is_integral<T>::value,
                "[MakeNdVector] The 1st argument must be an integer");
  return std::vector<decltype(MakeNdVector(std::forward<Args>(args)...))>(
      std::forward<T>(n), MakeNdVector(std::forward<Args>(args)...));
}

template <typename T, std::size_t N,
          typename std::enable_if<(N > 0), std::nullptr_t>::type = nullptr>
struct NdvectorImpl {
  using type = std::vector<typename NdvectorImpl<T, N - 1>::type>;
};  // struct ndvector_impl

template <typename T>
struct NdvectorImpl<T, 1> {
  using type = std::vector<T>;
};  // struct ndvector_impl

template <typename T, std::size_t N>
using NdVector = typename NdvectorImpl<T, N>::type;

#ifdef USE_STACK_TRACE_LOGGER
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Weverything"
#include <glog/logging.h>
#pragma clang diagnostic pop
#endif  //__clang__
#endif  // USE_STACK_TRACE_LOGGER

int64_t H, W, K, x1, x2, y1, y2;
vector<string> c;
vector<vector<int64_t>> use;
int64_t dx[] = {0, 1, 0, -1};
int64_t dy[] = {1, 0, -1, 0};

// bool Dfs(int64_t x, int64_t y) {
//   use[y][x] = true;
//   if (x == x2 && y == y2) {
//     return true;
//   }
//   bool ret = false;
//   rep(i, 4) {
//     int64_t x_ = x + dx[i];
//     int64_t y_ = y + dy[i];
//     if (x_ >= 0 && x_ < W && y_ >= 0 && y_ < H && !use[y_][x_] &&
//         c[y_][x_] == '.') {
//       ret |= Dfs(x_, y_);
//     }
//   }
//   return ret;
// }

template <typename T>
struct CoordinateCompress {
  vector<T> xs;

  CoordinateCompress() = default;
  CoordinateCompress(const vector<int64_t>& vs) { Add(vs); }
  CoordinateCompress(const initializer_list<vector<T>>& vs) {
    for (auto& v : vs) {
      Add(v);
    }
  }

  void Add(const vector<T>& vs) {
    size_t dn = vs.size();
    xs.reserve(xs.size() + dn);

    copy(vs.begin(), vs.end(), back_inserter(xs));
  }

  void Add(const T& x) { xs.emplace_back(x); }

  void Build(void) {
    sort(xs.begin(), xs.end());
    xs.erase(unique(xs.begin(), xs.end()), xs.end());
  }

  vector<int64_t> GetId(const vector<T>& vs) const {
    vector<int64_t> ret;
    ret.reserve(vs.size());
    transform(vs.begin(), vs.end(), back_inserter(ret), [&](const T& x) {
      return lower_bound(xs.begin(), xs.end(), x) - begin(xs);
    });
    return ret;
  }

  int64_t GetId(const T& x) const {
    return lower_bound(xs.begin(), xs.end(), x) - begin(xs);
  }

  const T& operator[](const int64_t k) const { return xs[k]; }
};

signed main(int argc, char* argv[]) {
  (void)argc;
#ifdef USE_STACK_TRACE_LOGGER
  google::InitGoogleLogging(argv[0]);
  google::InstallFailureSignalHandler();
#else
  (void)argv;
#endif  // USE_STACK_TRACE_LOGGER
  In(H, W, K, x1, y1, x2, y2);
  x1--;
  y1--;
  x2--;
  y2--;

  c.resize(H);
  rep(i, H) { In(c[i]); }

  auto inside = [&](const int64_t x, const int64_t y) {
    return (0 <= x && x < H && 0 <= y && y < W);
  };

  const int64_t kInf = numeric_limits<int64_t>::max() / 3;

  using P = pair<int64_t, int64_t>;
  queue<P> que;
  que.emplace(x1, y1);
  auto dist    = MakeNdVector(H, W, kInf);
  dist[x1][y1] = 0;

  while (!que.empty()) {
    auto [x, y] = que.front();
    que.pop();

    rep(k, 4) {
      rep(d, 1, K + 1) {
        int64_t x_ = x + d * dx[k];
        int64_t y_ = y + d * dy[k];
        if (!inside(x_, y_) || c[x_][y_] == '@' || dist[x_][y_] <= dist[x][y])
          break;
        dist[x_][y_] = dist[x][y] + 1;
        que.emplace(x_, y_);
      }
    }
  }
  if (dist[x2][y2] == kInf) {
    cout << -1 << endl;
  } else {
    cout << dist[x2][y2] << endl;
  }

  return EXIT_SUCCESS;
}


Compiler output:
a.cc:164:26: warning: built-in function 'y1' declared as non-function [-Wbuiltin-declaration-mismatch]
  164 | int64_t H, W, K, x1, x2, y1, y2;
      |                          ^~
a.cc: In function 'int main(int, char**)':
a.cc:250:24: error: 'numeric_limits' was not declared in this scope
  250 |   const int64_t kInf = numeric_limits<int64_t>::max() / 3;
      |                        ^~~~~~~~~~~~~~
a.cc:250:46: error: expected primary-expression before '>' token
  250 |   const int64_t kInf = numeric_limits<int64_t>::max() / 3;
      |                                              ^
a.cc:250:52: error: no matching function for call to 'max()'
  250 |   const int64_t kInf = numeric_limits<int64_t>::max() / 3;
      |                                               ~~~~~^~
In file included from /usr/include/c++/14/algorithm:60,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 0 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   candidate expects 2 arguments, 0 provided