this post was submitted on 08 Dec 2025
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Advent Of Code

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An unofficial home for the advent of code community on programming.dev! Other challenges are also welcome!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

Everybody Codes is another collection of programming puzzles with seasonal events.

EC 2025

AoC 2025

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🤶 - 2025 DAY 8 SOLUTIONS - 🤶 (programming.dev)
submitted 2 weeks ago by CameronDev@programming.dev to c/advent_of_code@programming.dev
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Day 8: Playground

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[–] CameronDev@programming.dev 2 points 2 weeks ago

Rust

Not an easy one, mostly because I messed up my merge circuits function (Pop/remove first circuit, load into second, but the pop/remove messed up the indexes, so I was merging the wrong thing).

After getting that it was all good. Pt2 was trivial once pt1 was solved.

spoiler

    #[derive(Debug)]
    struct Circuits {
        circuits: Vec<Vec<usize>>,
    }

    impl Circuits {
        fn find_circuit(&mut self, i: usize) -> Option<usize> {
            for (j, c) in &mut self.circuits.iter().enumerate() {
                if c.contains(&i) {
                    return Some(j);
                }
            }
            None
        }

        fn new_circuit(&mut self, i: usize, j: usize) {
            self.circuits.push(vec![i, j]);
        }

        fn join_circuits(&mut self, i: usize, j: usize) {
            let mut other = self.circuits.get(j).unwrap().clone();
            self.circuits.get_mut(i).unwrap().append(&mut other);
            self.circuits.remove(j);
        }

        fn append_circuit(&mut self, c: usize, x: usize) {
            self.circuits.get_mut(c).unwrap().push(x);
        }

        fn top_three(&mut self) -> Vec<usize> {
            let mut sizes = self
                .circuits
                .iter()
                .map(|c| c.len())
                .collect::<Vec<usize>>();
            sizes.sort();
            sizes.reverse();
            sizes[0..3].to_vec()
        }
    }

    type Pole = (isize, isize, isize);

    fn dist_poles(p1: &Pole, p2: &Pole) -> f32 {
        sqrt(
            ((p1.0 - p2.0) * (p1.0 - p2.0)) as f32
                + ((p1.1 - p2.1) * (p1.1 - p2.1)) as f32
                + ((p1.2 - p2.2) * (p1.2 - p2.2)) as f32,
        )
    }

    #[test]
    fn test_y2025_day8_part1() {
        let input = include_str!("../../input/2025/day_8.txt");
        let poles = input
            .lines()
            .map(|l| {
                let [x, y, z] = l
                    .splitn(3, ",")
                    .map(|c| c.parse::<isize>().unwrap())
                    .collect::<Vec<isize>>()[..]
                else {
                    panic!();
                };
                (x, y, z)
            })
            .collect::<Vec<Pole>>();
        let len = poles.len();

        let mut circuits: Circuits = Circuits { circuits: vec![] };

        let mut pairs = vec![];

        for i in 0..len {
            let first = poles.get(i).unwrap();
            for j in i + 1..len {
                if i == j {
                    continue;
                }
                let second = poles.get(j).unwrap();
                let dist = dist_poles(first, second);
                pairs.push((dist, i, j));
            }
        }

        pairs.sort_by(|a, b| {
            if a.0 < b.0 {
                Ordering::Less
            } else {
                Ordering::Greater
            }
        });

        for (dist, a, b) in pairs[0..1000].iter() {
            let first_circuit = circuits.find_circuit(*a);
            let second_circuit = circuits.find_circuit(*b);

            match (first_circuit, second_circuit) {
                (None, None) => {
                    circuits.new_circuit(*a, *b);
                }
                (Some(c), None) => {
                    circuits.append_circuit(c, *b);
                }
                (None, Some(c)) => {
                    circuits.append_circuit(c, *a);
                }
                (Some(c1), Some(c2)) => {
                    if c1 != c2 {
                        circuits.join_circuits(c1, c2);
                    }
                }
            }
        }

        assert_eq!(circuits.top_three().iter().product::<usize>(), 66640)
    }