From 262c339920b071d2e6515390ba13ddace7c9cd84 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Thu, 10 Nov 2022 11:11:02 -0800
Subject: [PATCH] 18

---
 2019/18.cpp | 56 ++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 36 insertions(+), 20 deletions(-)

diff --git a/2019/18.cpp b/2019/18.cpp
index 05f6d74..7274495 100644
--- a/2019/18.cpp
+++ b/2019/18.cpp
@@ -94,7 +94,7 @@ auto FindDistances(Map const& map, Features const& features) -> Distances {
   Distances distances;
 
   for (auto && [start_letter, start_coord] : features) {
-    if (islower(start_letter) || start_letter == '@') {
+    if (!std::isupper(start_letter)) {
       FindDistancesFrom(map, features, distances, start_letter, start_coord);
     }
   }
@@ -102,12 +102,6 @@ auto FindDistances(Map const& map, Features const& features) -> Distances {
   return distances;
 }
 
-struct P1S {
-  char location;
-  unsigned long long keys;
-  auto operator<=>(P1S const&) const = default;
-};
-
 auto HasKey(Doors doors, char key) {
   return doors.test(std::toupper(key) - 'A');
 }
@@ -116,26 +110,31 @@ auto SetKey(Doors doors, char key) {
   return doors.set(std::toupper(key) - 'A');
 }
 
-auto Part1(Distances const& distances) -> std::int64_t {
-  std::set<P1S> seen;
-  std::multimap<std::int64_t, std::pair<char, Doors>> todo
-    {{0, {'@', Doors()}}};
+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()}}};
 
   while (!todo.empty()) {
     auto it = todo.begin();
     auto [steps, ld] = *it;
-    auto& [l,keys] = ld;
+    auto& [locations,keys] = ld;
     todo.erase(it);
 
     if (keys.all()) { return steps; }
 
-    if (seen.insert({l,keys.to_ullong()}).second) {
-      auto dit = distances.find(l);
-      if (dit != distances.end()) {
-        for (auto && [next, costneed] : dit->second) {
+    if (seen.insert({locations,keys.to_ullong()}).second) {
+      for (auto location : locations) {
+        auto locations1 = locations; locations1.erase(location);
+
+        for (auto && [next, costneed] : distances.at(location)) {
           auto [cost, need] = costneed;
-          if ((need & (~keys)).none()) {
-            todo.insert({steps + cost, {next, SetKey(keys, next)}});
+          if ((need & ~keys).none()) {
+            auto locations2 = locations1; locations2.insert(next);
+            todo.insert({steps + cost, {locations2, SetKey(keys, next)}});
           }
         }
       }
@@ -145,6 +144,20 @@ auto Part1(Distances const& distances) -> std::int64_t {
   throw std::runtime_error{"no solution to part 1"};
 }
 
+auto UpdateMap(Map& map, Features & features) {
+  auto start = features['@'];
+  map[start.y][start.x] = '#';
+  map[start.y][start.x+1] = '#';
+  map[start.y][start.x-1] = '#';
+  map[start.y+1][start.x] = '#';
+  map[start.y-1][start.x] = '#';
+  features.erase('@');
+  features['^'] = Up(Left(start));
+  features['&'] = Down(Left(start));
+  features['*'] = Up(Right(start));
+  features['$'] = Down(Right(start));
+}
+
 } // namespace
 
 auto main(int argc, char** argv) -> int {
@@ -152,6 +165,9 @@ auto main(int argc, char** argv) -> int {
   auto features = FindFeatures(map);
   auto distances = FindDistances(map, features);
 
-  std::cout << "Part 1: " << Part1(distances) << std::endl;
-  //std::cout << "Part 2: " << part2 << std::endl;
+  std::cout << "Part 1: " << SolveMaze(distances, {'@'}) << std::endl;
+  
+  UpdateMap(map, features);
+  distances = FindDistances(map, features);
+  std::cout << "Part 2: " << SolveMaze(distances, {'^', '&', '*', '$'}) << std::endl;
 }