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๐ŸŽ„ - 2023 DAY 8 SOLUTIONS -๐ŸŽ„

Day 8: Haunted Wasteland

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  • First part was simple enough. Second part was easy logically, but after running the brute force solution with a parallel iterator from rayon and maxing out all 12 cores of this CPU, it was still taking forever. I always get tripped up by these ones that need fancy math, because although I was always good at math, I've never been good at looking at these problems and figuring out what kind of formula would apply. So I cheated and looked at other people's comments for their solutions, and saw the least common multiple mentioned. This made sense to me, so I implemented it and got a result almost instantly. I hate having to look at other comments to solve these things, but I never would have came to that conclusion myself.

    The code still isn't the cleanest, and I'd love to tidy up the parsing, but it works and I'm happy.

    https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day08.rs

    impl Solver for Day08 {
        fn star_one(&self, input: &str) -> String {
            let (directions, map) = input.split_once("\n\n").unwrap();
    
            let mut route_map = HashMap::new();
    
            for line in map.lines() {
                let line = line.replace(" ", "").replace("(", "").replace(")", "");
                let (position, destinations) = line.split_once('=').unwrap();
                let (left, right) = destinations.split_once(',').unwrap();
                route_map.insert(position.to_string(), (left.to_string(), right.to_string()));
            }
    
            let mut current_position = "AAA".to_string();
            for (step, direction) in directions.chars().cycle().enumerate() {
                current_position = match direction {
                    'L' => route_map[ยคt_position].0.to_string(),
                    'R' => route_map[ยคt_position].1.to_string(),
                    _ => unreachable!(),
                };
    
                if current_position == "ZZZ" {
                    return (step + 1).to_string();
                }
            }
    
            unreachable!()
        }
    
        fn star_two(&self, input: &str) -> String {
            let (directions, map) = input.split_once("\n\n").unwrap();
    
            let mut route_map = HashMap::new();
    
            for line in map.lines() {
                let line = line.replace(" ", "").replace("(", "").replace(")", "");
                let (position, destinations) = line.split_once('=').unwrap();
                let (left, right) = destinations.split_once(',').unwrap();
                route_map.insert(position.to_string(), (left.to_string(), right.to_string()));
            }
    
            let positions = route_map
                .keys()
                .filter(|pos| pos.ends_with('A'))
                .collect::>();
    
            let steps = positions
                .iter()
                .filter(|pos| pos.ends_with('A'))
                .map(|pos| {
                    let mut current_position = pos.to_string();
                    for (step, direction) in directions.chars().cycle().enumerate() {
                        current_position = match direction {
                            'L' => route_map[ยคt_position].0.to_string(),
                            'R' => route_map[ยคt_position].1.to_string(),
                            _ => unreachable!(),
                        };
    
                        if current_position.ends_with('Z') {
                            return step + 1;
                        }
                    }
                    unreachable!()
                })
                .collect::>();
    
            steps
                .into_iter()
                .reduce(|acc, steps| acc.lcm(&steps))
                .unwrap()
                .to_string()
        }
    }
    
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