2022-16

2022/16.cpp

@@ -6,10 +6,16 @@
 #include <tuple>
 #include <vector>
 #include <map>
+#include <unordered_map>
+#include <limits>
+
 #include <bitset>
 
 #include <boost/spirit/home/qi.hpp>
 #include <boost/range/irange.hpp>
+#include <boost/phoenix.hpp>
+#include <boost/range/algorithm.hpp>
+#include <boost/range/adaptor/map.hpp>
 
 #include <doctest.h>
 
@@ -47,42 +53,50 @@ auto Parse(std::istream & in) -> std::vector<RawRoom>
   std::vector<RawRoom> result;
   std::string line;
   while (std::getline(in, line)) {
-    RawRoom room;
-    using namespace boost::spirit;
+    namespace phx = boost::phoenix;
+    namespace qi = boost::spirit::qi;
+    using namespace qi::labels;
+    using It = std::string::const_iterator;
+
     auto const name = qi::as_string[+qi::alpha];
-    auto const room_description =
+
+    qi::rule<It, RawRoom()> room_description =
       "Valve " >>
-      name [ ([&](auto n) { room.name = n; }) ] >>
+      name [ phx::bind(&RawRoom::name, _val) = _1 ] >>
       " has flow rate=" >>
-      qi::ulong_long [ ([&](auto f) { room.flow = f; }) ] >>
+      qi::ulong_long [ phx::bind(&RawRoom::flow, _val) = _1 ] >>
       "; tunnel"  >> -qi::string("s") >>
       " lead"     >> -qi::string("s") >>
       " to valve" >> -qi::string("s") >>
       " " >>
-      (name % ", ") [ ([&](auto c) { room.connections = c; }) ];
+      (name % ", ") [ phx::bind(&RawRoom::connections, _val) = _1 ];
 
-    if (!qi::parse(line.begin(), line.end(), room_description)) {
+    It b = line.begin();
+    It e = line.end();
+    result.emplace_back();
+    if (!qi::parse(b, e, room_description, result.back())) {
       throw std::runtime_error{"bad input line"};
     }
-    result.emplace_back(std::move(room));
   }
   return result;
 }
 
-auto GenerateGraph(std::vector<RawRoom> const& raw_rooms) -> std::vector<Room>
+auto GenerateGraph(std::vector<RawRoom> const& raw_rooms) -> std::pair<std::size_t, std::vector<Room>>
 {
-  std::vector<Room> result;
-  std::map<std::string, std::size_t> names;
+  std::pair<std::size_t, std::vector<Room>> result {};
+  std::unordered_map<std::string, std::size_t> names;
 
   std::vector<std::vector<std::uint64_t>> distances(
-    raw_rooms.size(), std::vector<std::uint64_t>(raw_rooms.size(), 100)); // todo max limit
+    raw_rooms.size(), std::vector<std::uint64_t>(raw_rooms.size(), raw_rooms.size()));
   
   for (auto const i : boost::irange(raw_rooms.size())) {
     names[raw_rooms[i].name] = i;
+    if (raw_rooms[i].name == "AA") result.first = i;
   }
 
   for (auto const i : boost::irange(raw_rooms.size())) {
     auto & ds = distances[i];
+    ds[i] = 0;
     for (auto const& name : raw_rooms[i].connections) {
       ds[names[name]] = 1;
     }
@@ -91,7 +105,7 @@ auto GenerateGraph(std::vector<RawRoom> const& raw_rooms) -> std::vector<Room>
   ShortestDistances(distances);
 
   for (auto const i : boost::irange(raw_rooms.size())) {
-    result.push_back({raw_rooms[i].flow, std::move(distances[i])});
+    result.second.push_back({raw_rooms[i].flow, std::move(distances[i])});
   }
 
   return result;
@@ -106,37 +120,67 @@ struct State {
   Valves valves;
 };
 
-auto Routes(std::vector<Room> const& rooms, std::uint64_t time) -> std::map<unsigned long long, std::uint64_t>
+auto Routes(
+  std::size_t const start,
+  std::vector<Room> const& rooms, std::uint64_t initial_time
+) -> std::unordered_map<Valves, std::uint64_t>
 {
-  std::vector<State> states { State{time, 0, 0, {}} };
-  std::map<unsigned long long, std::uint64_t> result;
+  std::vector<State> states { State{initial_time, 0, start, {}} };
+  std::unordered_map<Valves, std::uint64_t> result;
   
   while (!states.empty()) {
-    auto state = states.back();
+    auto const state = states.back();
     states.pop_back();
 
     auto const& room = rooms[state.location];
 
     for (auto const i : boost::irange(rooms.size())) {
-      auto valves = state.valves;
-      if (valves[i]) { continue; }
-      auto const flow = rooms[i].flow;
-      if (flow == 0) { continue; }
-      auto const cost = room.connections[i];
-      if (cost >= state.time) { continue; }
-      auto const time_ = state.time - cost - 1;
-      
-      valves[i] = true;
-      auto const flow_ = state.flow + time_;
+      // don't revisit a valve
+      if (state.valves.test(i)) { continue; }
 
-      if (result[valves.to_ullong()] < flow_) {
-        result[valves.to_ullong()] = flow_;
+      // don't visit rooms with useless valves
+      if (rooms[i].flow == 0) { continue; }
+
+      // don't visit rooms we can't get to in time
+      auto const cost = room.connections[i];
+      if (cost+1 >= state.time) { continue; }
+
+      auto const time = state.time - cost - 1;      
+      auto const flow = state.flow + rooms[i].flow * time;
+      auto valves = state.valves;
+      valves.set(i);
+
+      // remember the best we've seen for this valve-set
+      if (result[valves] < flow) {
+        result[valves] = flow;
       }
 
-      states.push_back({ time_, state.flow + time_, i, valves});
+      states.push_back({time, flow, i, valves});
+    }
+  }
+
+  return result;
+}
+
+auto Part1(std::size_t start, std::vector<Room> const& rooms) -> std::uint64_t
+{
+  auto const routes = Routes(start, rooms, 30);
+  return *boost::range::max_element(routes | boost::adaptors::map_values);
+}
+
+auto Part2(std::size_t start, std::vector<Room> const& rooms) -> std::uint64_t
+{
+  auto const routes = Routes(start, rooms, 26);
+  auto const end = routes.end();
+  std::uint64_t result {0};
+  for (auto it1 = routes.begin(); it1 != end; std::advance(it1, 1)) {
+    for (auto it2 = std::next(it1); it2 != end; std::advance(it2, 1)) {
+      // only consider pairs that have disjoint sets of valves
+      if ((it1->first & it2->first).none()) {
+        result = std::max(result, it1->second + it2->second);
+      }
     }
   }
-  
   return result;
 }
 
@@ -145,22 +189,26 @@ auto Routes(std::vector<Room> const& rooms, std::uint64_t time) -> std::map<unsi
 TEST_SUITE("2022-16 examples") {
   TEST_CASE("example") {
     std::istringstream in {
- 
-    };
+R"(Valve AA has flow rate=0; tunnels lead to valves DD, II, BB
+Valve BB has flow rate=13; tunnels lead to valves CC, AA
+Valve CC has flow rate=2; tunnels lead to valves DD, BB
+Valve DD has flow rate=20; tunnels lead to valves CC, AA, EE
+Valve EE has flow rate=3; tunnels lead to valves FF, DD
+Valve FF has flow rate=0; tunnels lead to valves EE, GG
+Valve GG has flow rate=0; tunnels lead to valves FF, HH
+Valve HH has flow rate=22; tunnel leads to valve GG
+Valve II has flow rate=0; tunnels lead to valves AA, JJ
+Valve JJ has flow rate=21; tunnel leads to valve II
+)"};
+    auto const [start, graph] = GenerateGraph(Parse(in));
+    CHECK(1651 == Part1(start, graph));
+    CHECK(1707 == Part2(start, graph));
   }
 }
 
 auto main(int argc, char** argv) -> int
 {
-  auto const input = Parse(*aocpp::Startup(argc, argv));
-  auto const graph = GenerateGraph(input);
-  auto const routes = Routes(graph, 30);
-  
-  std::uint64_t p1 = 0;
-  for (auto const& kv : routes) {
-    p1 = std::max(p1, kv.second);
-  }
-
-  std::cout << "Part 1: " << p1 << std::endl;
-  //Part2(snapshots, std::cout << "Part 2:\n");
+  auto const [start, rooms] = GenerateGraph(Parse(*aocpp::Startup(argc, argv)));
+  std::cout << "Part 1: " << Part1(start, rooms) << std::endl;
+  std::cout << "Part 2: " << Part2(start, rooms) << std::endl;
 }