From 54605ed6a0ef3933fa6b2b780f2c37999e072b74 Mon Sep 17 00:00:00 2001
From: Lucas Resch <lucas.resch@gmx.de>
Date: Sat, 9 Dec 2023 12:57:25 +0100
Subject: [PATCH] 2023-08: Solve second puzzle

---
 2023-rust/README.md              | 15 +++++-----
 2023-rust/data/examples/08-2.txt | 10 +++++++
 2023-rust/src/bin/08.rs          | 47 ++++++++++++++++++++++++++++----
 3 files changed, 59 insertions(+), 13 deletions(-)
 create mode 100644 2023-rust/data/examples/08-2.txt

diff --git a/2023-rust/README.md b/2023-rust/README.md
index 6759861..e7fbcf4 100644
--- a/2023-rust/README.md
+++ b/2023-rust/README.md
@@ -9,15 +9,16 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 
 | Day | Part 1 | Part 2 |
 | :---: | :---: | :---:  |
-| [Day 1](./src/bin/01.rs) | `63.6µs` | `628.4µs` |
-| [Day 2](./src/bin/02.rs) | `43.1µs` | `49.8µs` |
-| [Day 3](./src/bin/03.rs) | `431.5µs` | `425.4µs` |
-| [Day 4](./src/bin/04.rs) | `96.6µs` | `19.2ms` |
+| [Day 1](./src/bin/01.rs) | `64.7µs` | `631.9µs` |
+| [Day 2](./src/bin/02.rs) | `41.3µs` | `47.5µs` |
+| [Day 3](./src/bin/03.rs) | `425.8µs` | `424.0µs` |
+| [Day 4](./src/bin/04.rs) | `97.7µs` | `19.5ms` |
 | [Day 5](./src/bin/05.rs) | `30.3µs` | `26.5s` |
-| [Day 6](./src/bin/06.rs) | `544.0ns` | `40.8ms` |
-| [Day 8](./src/bin/08.rs) | `259.2µs` | `-` |
+| [Day 6](./src/bin/06.rs) | `603.0ns` | `42.7ms` |
+| [Day 7](./src/bin/07.rs) | `202.3µs` | `-` |
+| [Day 8](./src/bin/08.rs) | `256.0µs` | `1.8ms` |
 
-**Total: 26562.00ms**
+**Total: 26566.19ms**
 <!--- benchmarking table --->
 
 ## Usage
diff --git a/2023-rust/data/examples/08-2.txt b/2023-rust/data/examples/08-2.txt
new file mode 100644
index 0000000..5b3fa58
--- /dev/null
+++ b/2023-rust/data/examples/08-2.txt
@@ -0,0 +1,10 @@
+LR
+
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)
diff --git a/2023-rust/src/bin/08.rs b/2023-rust/src/bin/08.rs
index 6833b1e..c64da44 100644
--- a/2023-rust/src/bin/08.rs
+++ b/2023-rust/src/bin/08.rs
@@ -11,11 +11,19 @@ enum Direction {
 
 pub fn part_one(input: &str) -> Option<u32> {
     let (directions, map) = parse_input(input);
+    solve_part_one("AAA", &directions, &map, |node| node == "ZZZ")
+}
 
-    let mut current_node = "AAA";
+fn solve_part_one(
+    starting_node: &str,
+    directions: &[Direction],
+    map: &HashMap<&str, (&str, &str)>,
+    end_condition: fn(&str) -> bool,
+) -> Option<u32> {
+    let mut current_node = starting_node;
     let mut steps: u32 = 0;
     for direction in directions.iter().cycle() {
-        if current_node == "ZZZ" {
+        if end_condition(current_node) {
             break;
         };
         steps += 1;
@@ -29,8 +37,33 @@ pub fn part_one(input: &str) -> Option<u32> {
     Some(steps)
 }
 
-pub fn part_two(input: &str) -> Option<u32> {
-    None
+pub fn part_two(input: &str) -> Option<u64> {
+    let (directions, map) = parse_input(input);
+
+    let steps_per_ghost = map
+        .keys()
+        .filter(|key| key.ends_with('A'))
+        .filter_map(|node| solve_part_one(node, &directions, &map, |node| node.ends_with('Z')))
+        .collect_vec();
+
+    Some(
+        steps_per_ghost
+            .iter()
+            .map(|steps| *steps as u64)
+            .fold(1, lcm),
+    )
+}
+
+fn gcd(a: u64, b: u64) -> u64 {
+    if b == 0 {
+        a
+    } else {
+        gcd(b, a % b)
+    }
+}
+
+fn lcm(a: u64, b: u64) -> u64 {
+    a / gcd(a, b) * b
 }
 
 fn parse_input(input: &str) -> (Vec<Direction>, HashMap<&str, (&str, &str)>) {
@@ -72,7 +105,9 @@ mod tests {
 
     #[test]
     fn test_part_two() {
-        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        let result = part_two(&advent_of_code::template::read_file_part(
+            "examples", DAY, 2,
+        ));
+        assert_eq!(result, Some(6));
     }
 }