From 76bd7d9c54712207d5258f4ce3bccdb03818a8dc Mon Sep 17 00:00:00 2001
From: Antoine Martin <antoine97.martin@gmail.com>
Date: Mon, 7 Dec 2020 16:14:03 +0100
Subject: [PATCH] 2020: day07: add note

---
 aoc2020/src/day07.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/aoc2020/src/day07.rs b/aoc2020/src/day07.rs
index a2e9a8c..37fd9d4 100644
--- a/aoc2020/src/day07.rs
+++ b/aoc2020/src/day07.rs
@@ -30,6 +30,9 @@ fn part1(input: &str) -> aoc::Result<usize> {
 
     let mut memoized = HashMap::new();
 
+    // NOTE: part 1 can also be solved efficiently by using a graph where a bag has its parents as
+    //       neighbours, and then by computing the size of the sub graph accessible from 'shiny
+    //       gold'
     Ok(bag_rules
         .iter()
         .filter(|bag| bag.can_contain("shiny gold", &bag_rules_map, &mut memoized))