From 3da0605201572e41500e187258f4995a1d03bbd2 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 23 Dec 2019 23:48:53 +0100
Subject: [PATCH] Speed up day 18 part 2.

---
 2019/src/day18.cpp | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/2019/src/day18.cpp b/2019/src/day18.cpp
index 1f912f8..e5c8452 100644
--- a/2019/src/day18.cpp
+++ b/2019/src/day18.cpp
@@ -155,7 +155,7 @@ void aoc2019::day18_part1(std::istream &input, std::ostream &output) {
 }
 
 void aoc2019::day18_part2(std::istream &input, std::ostream &output) {
-    using state_t = std::tuple<unsigned int, std::array<char, 4>>;
+    using state_t = std::pair<unsigned int, std::array<char, 4>>;
 
     auto map = read_map(input);
 
@@ -177,7 +177,7 @@ void aoc2019::day18_part2(std::istream &input, std::ostream &output) {
     const auto implied_graph = compute_implied_graph(map);
 
     std::priority_queue<std::pair<int, state_t>, std::vector<std::pair<int, state_t>>, std::greater<>> todo;
-    std::map<state_t, int> visited;
+    std::map<std::pair<unsigned int, char>, int> visited;
     todo.emplace(0, state_t(0, {'@', '*', '^', '/'}));
 
     auto target_size = std::count_if(implied_graph.cbegin(), implied_graph.cend(),
@@ -188,10 +188,6 @@ void aoc2019::day18_part2(std::istream &input, std::ostream &output) {
         const auto[dist, state] = todo.top();
         todo.pop();
 
-        if (visited[state] < dist) {
-            continue;
-        }
-
         auto[keys, pos] = state;
 
         if (std::__popcount(keys) == target_size) {
@@ -217,8 +213,8 @@ void aoc2019::day18_part2(std::istream &input, std::ostream &output) {
                 next_pos[i] = edge.first;
 
                 state_t next_state = {next_keys, next_pos};
-                if (auto it = visited.find(next_state); it == visited.end() || it->second > next_dist) {
-                    visited[next_state] = next_dist;
+                if (auto it = visited.find({next_keys, next_pos[i]}); it == visited.end() || it->second > next_dist) {
+                    visited[{next_keys, next_pos[i]}] = next_dist;
                     todo.emplace(next_dist, next_state);
                 }
             }