day8: finish by using LCM

2023/day8/Cargo.toml

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+num = "0.4.1"

2023/day8/src/main.rs

@@ -1,5 +1,7 @@
 use std::collections::HashMap;
 
+use num::integer::lcm;
+
 enum Direction {
  Left,
  Right,
@@ -63,48 +65,34 @@ fn part1(input: &str) -> usize {
  }
  count
 }
+
+/// from the subreddit, we can use the LCM algorithm (couldn't figure it out myself this time)
 fn part2(input: &str) -> usize {
  let map = Map::parse(input);
- let mut currents = map
+ let currents = map
  .network
  .keys()
  .filter(|k| k.ends_with('A'))
  .copied()
  .collect::<Vec<_>>();
- let mut directions = map.directions.iter().cycle();
- let mut count: usize = 0;
- while !currents.iter().all(|c| c.ends_with('Z')) {
- let direction = directions.next().unwrap();
- for current in currents.iter_mut() {
+ let mut lowest: usize = 0;
+ for mut current in currents {
+  let mut directions = map.directions.iter().cycle();
+ let mut count = 0;
+ while !current.ends_with('Z') {
  let node = map.network.get(current).unwrap();
- match direction {
- Direction::Left => *current = node.0,
- Direction::Right => *current = node.1,
- }
- if current.ends_with('Z') {
- println!("{}: {}", count, current);
+ count += 1;
+ match directions.next().unwrap() {
+ Direction::Left => current = node.0,
+ Direction::Right => current = node.1,
  }
  }
- count += 1;
+ match lowest {
+ 0 => lowest = count,
+ _ => lowest = lcm(lowest, count),
+ }
  }
-
- // let mut gcount: usize = 0;
- // for mut current in currents {
- // let mut directions = map.directions.iter().cycle();
- // let mut count = 0;
- // while !current.ends_with('Z') {
- // let node = map.network.get(current).unwrap();
- // count += 1;
- // match directions.next().unwrap() {
- // Direction::Left => current = node.0,
- // Direction::Right => current = node.1,
- // }
- // }
- // println!("count: {}", count);
- // gcount += count;
- // }
- // gcount
- count
+ lowest
 }
 fn main() {
  let input = include_str!("../input.txt");