18

2019/18.cpp

@@ -12,6 +12,7 @@
 #include <bitset>
 #include <deque>
 #include <cctype>
+#include <queue>
 #include <map>
 
 #include <aocpp/Startup.hpp>
@@ -110,19 +111,33 @@ auto SetKey(Doors doors, char key) {
   return doors.set(std::toupper(key) - 'A');
 }
 
-auto SolveMaze(Distances const& distances, std::set<char> const initial_locations) -> std::int64_t {
+template <class Elt, class Compare>
+auto MakePQueue(Compare const& compare)
+  -> std::priority_queue<Elt, std::vector<Elt>, Compare>
+{
+  return {compare};
+}
+
+auto SolveMaze(
+  Distances const& distances,
+  std::set<char> const initial_locations
+) -> std::int64_t
+{
   // Track current positions and current set of keys in easy to compare form
   using Visited = std::pair<std::set<char>, unsigned long long>;
   std::set<Visited> seen;
 
-  std::multimap<std::int64_t, std::pair<std::set<char>, Doors>> todo
-    {{0, {initial_locations, Doors()}}};
+  auto todo = MakePQueue<std::tuple<std::int64_t, std::set<char>, Doors>>(
+    [](auto const& x, auto const& y) {
+      return std::get<0>(x) > std::get<0>(y);
+    }
+  );
+
+  todo.emplace(0, initial_locations, Doors());
 
   while (!todo.empty()) {
-    auto it = todo.begin();
-    auto [steps, ld] = *it;
-    auto& [locations,keys] = ld;
-    todo.erase(it);
+    auto [steps, locations, keys] = todo.top();
+    todo.pop();
 
     if (keys.all()) { return steps; }
 
@@ -134,7 +149,7 @@ auto SolveMaze(Distances const& distances, std::set<char> const initial_location
           auto [cost, need] = costneed;
           if ((need & ~keys).none()) {
             auto locations2 = locations1; locations2.insert(next);
-            todo.insert({steps + cost, {locations2, SetKey(keys, next)}});
+            todo.emplace(steps + cost, locations2, SetKey(keys, next));
           }
         }
       }