From 3d665e5ebb5fcf91b60f6587c5e1006c842db320 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Thu, 10 Nov 2022 21:25:27 -0800
Subject: [PATCH] Update 20.cpp

---
 2019/20.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/2019/20.cpp b/2019/20.cpp
index 95525cc..638f298 100644
--- a/2019/20.cpp
+++ b/2019/20.cpp
@@ -118,11 +118,11 @@ auto FindDistances(Map const& map, Portals const& portals) {
   Distances distances;
 
   std::map<Coord, Name> names;
-  for (auto [k,v] : portals) {
+  for (auto const& [k,v] : portals) {
     names[v] = k;
   }
 
-  for (auto const [start_name, start_coord] : portals) {
+  for (auto const& [start_name, start_coord] : portals) {
     distances[start_name] = FindDistancesFrom(map, names, distances, start_name, start_coord);
   }
 
@@ -132,11 +132,11 @@ auto FindDistances(Map const& map, Portals const& portals) {
 auto SolveMaze(Distances const& distances, bool const recursive) -> std::int64_t
 {
   // Track current positions and current set of keys in easy to compare form
-  using Visited = std::pair<int, Name>;
+  using Visited = std::pair<std::int64_t, Name>;
   std::set<Visited> seen;
 
   // Priority queue returning lowest path cost states first.
-  using PqElt = std::tuple<std::int64_t, int, Name>;
+  using PqElt = std::tuple<std::int64_t, std::int64_t, Name>;
   using PqCmp = decltype([](PqElt const& x, PqElt const& y) {
                 return std::get<0>(x) > std::get<0>(y); });
   std::priority_queue<PqElt, std::vector<PqElt>, PqCmp> todo;
@@ -144,7 +144,7 @@ auto SolveMaze(Distances const& distances, bool const recursive) -> std::int64_t
   todo.emplace(0, 0, "-AA");
 
   while(!todo.empty()) {
-    auto [steps, depth, name] = todo.top();
+    auto const [steps, depth, name] = todo.top();
     todo.pop();
     if (name == "-ZZ") { return steps; }
     if (seen.emplace(depth, name).second) {