16

2022/16.cpp

@@ -34,6 +34,12 @@ namespace {
 namespace phx = boost::phoenix;
 namespace qi = boost::spirit::qi;
 
+/// @brief The starting room as defined in the problem statement
+constexpr char const* STARTING_ROOM = "AA";
+
+/// @brief Arbitrary number of valves this solution supports
+constexpr std::size_t MAX_VALVES = 64;
+
 /// @brief Array of distances from one node to another.
 /// @tparam T distance type
 ///
@@ -55,15 +61,14 @@ auto ShortestDistances(distance_array<T> & dist) -> void
   for (auto const k : range) {
     for (auto const i : range) {
       for (auto const j : range) {
-        auto const new_dist = dist[i][k] + dist[k][j];
+        auto const d_ikj = dist[i][k] + dist[k][j];
-        auto & old_dist = dist[i][j];
+        auto & d_ij = dist[i][j];
-        if (old_dist > new_dist) old_dist = new_dist;
+        if (d_ij > d_ikj) d_ij = d_ijk;
       }
     }
   }
 }
 
-/// @struct Room
 /// @brief A single record from the problem input.
 struct Room {
   /// @brief Name of the room
@@ -122,7 +127,6 @@ auto FlowsFirst(
 ) -> std::size_t
 {
   using namespace phx::placeholders;
-
   auto const zeros = boost::range::partition(rooms, phx::bind(&Room::flow, arg1) > 0);
   return std::distance(boost::begin(rooms), zeros);
 }
@@ -134,7 +138,7 @@ auto GenerateDistances(
   std::vector<Room> const& rooms
 ) -> std::pair<std::size_t, distance_array<std::uint64_t>>
 {
-  auto const N = rooms.size();
+  auto const N {rooms.size()};
 
   // Associate the names and indexes of each room
   std::unordered_map<std::string, std::size_t> names;
@@ -144,15 +148,14 @@ auto GenerateDistances(
 
   distance_array<std::uint64_t> distances{boost::extents[N][N]};
 
-  // N is longer than any optimal distance by at least 1
-  std::fill_n(distances.data(), distances.num_elements(), N);
-
   for (auto const i : boost::irange(rooms.size())) {
-    auto & room = rooms[i];
     auto di = distances[i];
   
+    // Default value: N is longer than any optimal distance by at least 1
+    boost::range::fill(di, N);
+
     // each room is one away from adjacent rooms
-    for (auto const& name : room.connections) {
+    for (auto const& name : rooms[i].connections) {
       di[names[name]] = 1;
     }
 
@@ -162,13 +165,12 @@ auto GenerateDistances(
 
   ShortestDistances(distances);
 
-  return {names.at("AA"), std::move(distances)};
+  return {names.at(STARTING_ROOM), std::move(distances)};
 }
 
 /// @brief Bitset used to track which valves have been turned on
-using Valves = std::bitset<64>;
+using Valves = std::bitset<MAX_VALVES>;
 
-/// @struct State
 /// @brief Intermediate states for depth-first search in Routes
 struct State {
   /// @brief Time remaining
@@ -194,11 +196,15 @@ auto Routes(
   distance_array<std::uint64_t> const& distances
 ) -> std::unordered_map<Valves, std::uint64_t>
 {
+  if (rooms.size() > MAX_VALVES) {
+    throw std::runtime_error{"Too many valves"};
+  }
+
   // Maximal flow seen at each set of open valves
   std::unordered_map<Valves, std::uint64_t> result;
 
   // Remaining states for depth first search
-  std::vector<State> states { State{initial_time, 0, start, {}} };
+  std::vector<State> states {{initial_time, 0, start, {}}};
   while (!states.empty()) {
     auto const state = states.back();
     states.pop_back();

lib/src/Startup.cpp

@@ -53,12 +53,12 @@ namespace
       case 't':
         result.run_tests = true;
         break;
-      case ':':
-        std::cerr << "Missing argument to -" << char(optopt) << std::endl;
-        return {};
       case 'h':
         result.print_help = true;
         break;
+      case ':':
+        std::cerr << "Missing argument to -" << char(optopt) << std::endl;
+        return {};
       case '?':
       default:
         std::cerr << "Unknown flag -" << char(optopt) << std::endl;