[2025] Day 8 draft

Author: connorslade

README.md

@@ -12,6 +12,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 05: Cafeteria](aoc_2025/src/day_05.rs)
 - [Day 06: Trash Compactor](aoc_2025/src/day_06.rs)
 - [Day 07: Laboratories](aoc_2025/src/day_07.rs)
+- [Day 08: Playground](aoc_2025/src/day_08.rs)
 <!-- MARKER -->
 
 ## [2024](https://adventofcode.com/2024) [![aoc_2024](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2024.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2024.yml)

aoc_2025/src/day_08.rs

@@ -0,0 +1,176 @@
+use std::{
+    collections::{HashMap, HashSet},
+    iter::repeat_n,
+};
+
+use common::{Answer, solution};
+use itertools::Itertools;
+use nd_vec::{Vec3, vector};
+
+solution!("Playground", 8);
+
+fn part_a(input: &str) -> Answer {
+    let boxes = input
+        .lines()
+        .map(|x| {
+            let mut coords = x.split(',').map(|x| x.parse::<i64>().unwrap());
+            vector!(
+                coords.next().unwrap(),
+                coords.next().unwrap(),
+                coords.next().unwrap()
+            )
+        })
+        .collect::<Vec<_>>();
+
+    let mut closest_paris = boxes
+        .iter()
+        .combinations(2)
+        .map(|x| ((*x[0] - *x[1]).magnitude_squared(), (*x[0], *x[1])))
+        .collect::<Vec<_>>();
+    closest_paris.sort_by_key(|x| x.0);
+
+    let mut connections = HashMap::new();
+    for (_dist, (a, b)) in closest_paris.iter().take(1000) {
+        println!("connecting {a:?} and {b:?}");
+
+        connections.entry(*a).or_insert(HashSet::new()).insert(*b);
+        connections.entry(*b).or_insert(HashSet::new()).insert(*a);
+    }
+
+    // get the length of every unique sub graph
+    fn subgraph_size(
+        connections: &HashMap<Vec3<i64>, HashSet<Vec3<i64>>>,
+        seen: &mut HashSet<Vec3<i64>>,
+        node: Vec3<i64>,
+    ) -> u64 {
+        if !seen.insert(node) {
+            return 0;
+        }
+
+        let children = &connections[&node];
+
+        let mut out = 1;
+        for child in children {
+            out += subgraph_size(connections, seen, *child);
+        }
+
+        out
+    }
+
+    let mut seen = HashSet::new();
+    let mut sizes = Vec::new();
+    for start in connections.keys() {
+        let size = subgraph_size(&connections, &mut seen, *start);
+        if size > 0 {
+            sizes.push(size);
+            println!("{start:?} is in a {size} node circuit");
+        }
+    }
+
+    let unconnected = boxes.iter().filter(|x| !seen.contains(x)).count();
+    sizes.extend(repeat_n(1, unconnected));
+
+    sizes.sort();
+
+    sizes.iter().rev().take(3).product::<u64>().into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let boxes = input
+        .lines()
+        .map(|x| {
+            let mut coords = x.split(',').map(|x| x.parse::<i64>().unwrap());
+            vector!(
+                coords.next().unwrap(),
+                coords.next().unwrap(),
+                coords.next().unwrap()
+            )
+        })
+        .collect::<Vec<_>>();
+
+    let mut closest_paris = boxes
+        .iter()
+        .combinations(2)
+        .map(|x| ((*x[0] - *x[1]).magnitude_squared(), (*x[0], *x[1])))
+        .collect::<Vec<_>>();
+    closest_paris.sort_by_key(|x| x.0);
+
+    let mut connections = HashMap::new();
+    for (_dist, (a, b)) in closest_paris.iter() {
+        connections.entry(*a).or_insert(HashSet::new()).insert(*b);
+        connections.entry(*b).or_insert(HashSet::new()).insert(*a);
+
+        //
+
+        let mut seen = HashSet::new();
+        for start in connections.keys() {
+            subgraph_size(&connections, &mut seen, *start);
+        }
+
+        let unconnected = boxes.iter().filter(|x| !seen.contains(x)).count();
+
+        if unconnected == 0 {
+            return (a.x() * b.x()).into();
+        }
+    }
+
+    // get the length of every unique sub graph
+    fn subgraph_size(
+        connections: &HashMap<Vec3<i64>, HashSet<Vec3<i64>>>,
+        seen: &mut HashSet<Vec3<i64>>,
+        node: Vec3<i64>,
+    ) -> u64 {
+        if !seen.insert(node) {
+            return 0;
+        }
+
+        let children = &connections[&node];
+
+        let mut out = 1;
+        for child in children {
+            out += subgraph_size(connections, seen, *child);
+        }
+
+        out
+    }
+
+    ().into()
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        162,817,812
+        57,618,57
+        906,360,560
+        592,479,940
+        352,342,300
+        466,668,158
+        542,29,236
+        431,825,988
+        739,650,466
+        52,470,668
+        216,146,977
+        819,987,18
+        117,168,530
+        805,96,715
+        346,949,466
+        970,615,88
+        941,993,340
+        862,61,35
+        984,92,344
+        425,690,689
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 40.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 25272.into());
+    }
+}

aoc_2025/src/lib.rs

@@ -7,6 +7,7 @@ mod day_04;
 mod day_05;
 mod day_06;
 mod day_07;
+mod day_08;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -17,5 +18,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_05::SOLUTION,
     day_06::SOLUTION,
     day_07::SOLUTION,
+    day_08::SOLUTION,
     // [list_marker]
 ];