16

2022/16.cpp

@@ -31,6 +31,9 @@
 
 namespace {
 
+namespace phx = boost::phoenix;
+namespace qi = boost::spirit::qi;
+
 /// @brief Array of distances from one node to another.
 /// @tparam T distance type
 ///
@@ -85,8 +88,6 @@ auto Parse(std::istream & in) -> std::vector<Room>
   std::vector<Room> result;
   std::string line;
   while (std::getline(in, line)) {
-    namespace phx = boost::phoenix;
-    namespace qi = boost::spirit::qi;
     using namespace qi::labels;
     using It = std::string::const_iterator;
 
@@ -120,8 +121,10 @@ auto FlowsFirst(
   std::vector<Room> & rooms
 ) -> std::size_t
 {
-  auto const zeros = boost::range::partition(rooms, [](auto const& room) { return room.flow > 0; });
-  return zeros - rooms.begin();
+  using namespace phx::placeholders;
+
+  auto const zeros = boost::range::partition(rooms, phx::bind(&Room::flow, arg1) > 0);
+  return std::distance(boost::begin(rooms), zeros);
 }
 
 /// @brief Computes the distances between rooms and finds the address of the starting room
@@ -144,7 +147,8 @@ auto GenerateDistances(
   // N is longer than any optimal distance by at least 1
   std::fill_n(distances.data(), distances.num_elements(), N);
 
-  for (auto [i, room] : rooms | boost::adaptors::indexed()) {
+  for (auto const i : boost::irange(rooms.size())) {
+    auto & room = rooms[i];
     auto di = distances[i];
 
     // each room is one away from adjacent rooms
@@ -185,7 +189,6 @@ struct State {
 /// @return Mapping of maximum flow achievable using a particular set of valves
 auto Routes(
   std::size_t const start,
-  std::size_t const interesting,
   std::uint64_t const initial_time,
   std::vector<Room> const& rooms,
   distance_array<std::uint64_t> const& distances
@@ -206,7 +209,7 @@ auto Routes(
 
     auto const distances_i = distances[state.location];
 
-    for (auto const j : boost::irange(interesting)) {
+    for (auto const [j, room] : rooms | boost::adaptors::indexed()) {
       // don't revisit a valve
       if (state.valves.test(j)) { continue; }
 
@@ -216,7 +219,7 @@ auto Routes(
       if (cost >= state.time) { continue; }
 
       auto const time = state.time - cost;
-      auto const flow = state.flow + rooms[j].flow * time;
+      auto const flow = state.flow + room.flow * time;
       auto valves = state.valves;
       valves.set(j);
 
@@ -234,33 +237,31 @@ auto Routes(
 /// @return Maximum flow achievable
 auto Part1(
   std::size_t const start,
-  std::size_t const interesting,
   std::vector<Room> const& rooms,
   distance_array<std::uint64_t> const& distances
 ) -> std::uint64_t
 {
-  auto const routes = Routes(start, interesting, 30, rooms, distances);
+  auto const routes = Routes(start, 30, rooms, distances);
   return *boost::range::max_element(routes | boost::adaptors::map_values);
 }
 
-/// @brief Maximize the water flow using two actos and 26 minutes
+/// @brief Maximize the water flow using two actors and 26 minutes
 /// @param[in] start Index of the starting room
 /// @param[in] rooms Rooms from input file
 /// @param[in] distances Shortest distances between pairs of rooms
 /// @return Maximum flow achievable
 auto Part2(
   std::size_t const start,
-  std::size_t const interesting,
   std::vector<Room> const& rooms,
   distance_array<std::uint64_t> const& distances
 ) -> std::uint64_t
 {
-  auto const routes = Routes(start, interesting, 26, rooms, distances);
+  auto const routes = Routes(start, 26, rooms, distances);
   auto const end = routes.end();
   
   std::uint64_t best {0};
-  for (auto it1 = routes.begin(); it1 != end; std::advance(it1, 1)) {
-    for (auto it2 = std::next(it1); it2 != end; std::advance(it2, 1)) {
+  for (auto it1 = routes.begin(); it1 != end; ++it1) {
+    for (auto it2 = std::next(it1); it2 != end; ++it2) {
       // only consider pairs that have disjoint sets of valves
       if ((it1->first & it2->first).none()) {
         best = std::max(best, it1->second + it2->second);
@@ -287,10 +288,11 @@ Valve II has flow rate=0; tunnels lead to valves AA, JJ
 Valve JJ has flow rate=21; tunnel leads to valve II
 )"};
     auto rooms = Parse(in);
-    auto const interesting = FlowsFirst(rooms);
+    auto const n = FlowsFirst(rooms);
     auto const [start, distances] = GenerateDistances(rooms);
-    CHECK(1651 == Part1(start, interesting, rooms, distances));
-    CHECK(1707 == Part2(start, interesting, rooms, distances));
+    rooms.resize(n);
+    CHECK(1651 == Part1(start, rooms, distances));
+    CHECK(1707 == Part2(start, rooms, distances));
   }
 
   TEST_CASE("shortest path") {
@@ -339,6 +341,7 @@ auto main(int argc, char** argv) -> int
   auto rooms = Parse(*aocpp::Startup(argc, argv));
   auto const n = FlowsFirst(rooms);
   auto const [start, distances] = GenerateDistances(rooms);
-  std::cout << "Part 1: " << Part1(start, n, rooms, distances) << std::endl;
-  std::cout << "Part 2: " << Part2(start, n, rooms, distances) << std::endl;
+  rooms.resize(n);
+  std::cout << "Part 1: " << Part1(start, rooms, distances) << std::endl;
+  std::cout << "Part 2: " << Part2(start, rooms, distances) << std::endl;
 }