cses graphs

cses/graph-algorithms/labyrinth.cc

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+#include <bits/stdc++.h>  // {{{
+
+#include <version>
+#ifdef __cpp_lib_ranges_enumerate
+#include <ranges>
+namespace rv = std::views;
+namespace rs = std::ranges;
+#endif
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using f64 = double;
+using f128 = long double;
+
+#if __cplusplus >= 202002L
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+#endif
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+template <typename T>
+using vec = std::vector<T>;
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+#define ff first
+#define ss second
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+unordered_map<char, pair<i32, i32>> dirs{
+    {'L', {0, -1}}, {'R', {0, 1}}, {'U', {-1, 0}}, {'D', {1, 0}}};
+
+void solve() {
+  u32 n, m;
+  cin >> n >> m;
+
+  vec<string> grid(n);
+  for (auto& e : grid)
+    cin >> e;
+
+  i32 sr, sc, er, ec;
+  for (u32 r = 0; r < n; ++r) {
+    for (u32 c = 0; c < m; ++c) {
+      if (grid[r][c] == 'A') {
+        sr = r;
+        sc = c;
+      } else if (grid[r][c] == 'B') {
+        er = r;
+        ec = c;
+      }
+    }
+  }
+
+  queue<pair<i32, i32>> q{{{sr, sc}}};
+  vec<string> trace(n, string(m, ' '));
+
+  auto print_trace = [&]() mutable -> void {
+    string ans;
+    i32 row = er, col = ec;
+
+    while (grid[row][col] != 'A') {
+      char step = trace[row][col];
+      ans.push_back(step);
+      row -= dirs.at(step).first;
+      col -= dirs.at(step).second;
+    }
+
+    reverse(all(ans));
+    cout << ans.size() << '\n' << ans << '\n';
+  };
+
+  while (!q.empty()) {
+    auto [r, c] = q.front();
+    q.pop();
+
+    if (r == er && c == ec) {
+      cout << "YES\n";
+      print_trace();
+      return;
+    }
+
+    for (auto& [letter, dir] : dirs) {
+      auto& [dr, dc] = dir;
+      i32 nr = r + dr;
+      i32 nc = c + dc;
+
+      if (min(nr, nc) < 0 || nr >= n || nc >= m || grid[nr][nc] == '#' ||
+          trace[nr][nc] != ' ') {
+        continue;
+      }
+
+      trace[nr][nc] = letter;
+      q.emplace(nr, nc);
+    }
+  }
+
+  cout << "NO\n";
+}
+
+int main() {  // {{{
+  std::cin.exceptions(std::cin.failbit);
+
+#ifdef LOCAL
+  std::cerr.rdbuf(std::cout.rdbuf());
+  std::cout.setf(std::ios::unitbuf);
+  std::cerr.setf(std::ios::unitbuf);
+#else
+  std::cin.tie(nullptr)->sync_with_stdio(false);
+#endif
+
+  u32 tc = 1;
+  // std::cin >> tc;
+
+  for (u32 t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}