Year 2025 Day 8

Author: maneatingape

README.md

@@ -84,6 +84,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 5 | [Cafeteria](https://adventofcode.com/2025/day/5) | [Source](src/year2025/day05.rs) | 20 |
 | 6 | [Trash Compactor](https://adventofcode.com/2025/day/6) | [Source](src/year2025/day06.rs) | 20 |
 | 7 | [Laboratories](https://adventofcode.com/2025/day/7) | [Source](src/year2025/day07.rs) | 5 |
+| 8 | [Playground](https://adventofcode.com/2025/day/8) | [Source](src/year2025/day08.rs) | 13000 |
 
 ## 2024
 

benches/benchmark.rs

@@ -95,5 +95,5 @@ benchmark!(year2024
 );
 
 benchmark!(year2025
-    day01, day02, day03, day04, day05, day06, day07
+    day01, day02, day03, day04, day05, day06, day07, day08
 );

src/lib.rs

@@ -74,5 +74,5 @@ library!(year2024 "Locate the Chief Historian in time for the big Christmas slei
 );
 
 library!(year2025 "Finish the North Pole decorations in time for Christmas."
-    day01, day02, day03, day04, day05, day06, day07
+    day01, day02, day03, day04, day05, day06, day07, day08
 );

src/main.rs

@@ -141,5 +141,5 @@ run!(year2024
 );
 
 run!(year2025
-    day01, day02, day03, day04, day05, day06, day07
+    day01, day02, day03, day04, day05, day06, day07, day08
 );

src/year2025/day08.rs

@@ -0,0 +1,69 @@
+//! # Playground
+use crate::util::iter::*;
+use crate::util::parse::*;
+
+type Box = [u64; 3];
+type Pair = (usize, usize, u64);
+type Input = (Vec<Box>, Vec<Pair>);
+
+pub fn parse(input: &str) -> Input {
+    let boxes: Vec<_> = input.iter_unsigned::<u64>().chunk::<3>().collect();
+    let mut pairs = Vec::with_capacity(boxes.len() * (boxes.len() - 1));
+
+    for (i, &v1) in boxes.iter().enumerate() {
+        for (j, &v2) in boxes.iter().enumerate().skip(i + 1) {
+            let dx = v1[0].abs_diff(v2[0]);
+            let dy = v1[1].abs_diff(v2[1]);
+            let dz = v1[2].abs_diff(v2[2]);
+            let distance = dx * dx + dy * dy + dz * dz;
+            pairs.push((i, j, distance));
+        }
+    }
+
+    pairs.sort_unstable_by_key(|&(.., distance)| distance);
+    (boxes, pairs)
+}
+
+pub fn part1(input: &Input) -> usize {
+    part1_testable(input, 1000)
+}
+
+pub fn part1_testable(input: &Input, limit: usize) -> usize {
+    let (boxes, pairs) = input;
+    let mut sets: Vec<_> = (0..boxes.len()).map(|i| vec![i]).collect();
+
+    for (i, j, ..) in pairs.iter().take(limit) {
+        let first = (0..sets.len()).find(|&k| sets[k].contains(i)).unwrap();
+        let second = (0..sets.len()).find(|&k| sets[k].contains(j)).unwrap();
+
+        let min = first.min(second);
+        let max = first.max(second);
+
+        if min != max {
+            let other = sets.remove(max);
+            sets[min].extend(other);
+        }
+    }
+
+    let mut sizes: Vec<_> = sets.iter().map(Vec::len).collect();
+    sizes.sort_unstable();
+    sizes.iter().rev().take(3).product()
+}
+
+pub fn part2(input: &Input) -> u64 {
+    let (boxes, pairs) = input;
+    let mut seen = vec![false; boxes.len()];
+    let mut remaining = boxes.len();
+
+    for &(i, j, _) in pairs {
+        remaining -= usize::from(!seen[i]) + usize::from(!seen[j]);
+        seen[i] = true;
+        seen[j] = true;
+
+        if remaining == 0 {
+            return boxes[i][0] * boxes[j][0];
+        }
+    }
+
+    unreachable!()
+}

tests/test.rs

@@ -87,5 +87,5 @@ test!(year2024
 );
 
 test!(year2025
-    day01, day02, day03, day04, day05, day06, day07
+    day01, day02, day03, day04, day05, day06, day07, day08
 );

tests/year2025/day08.rs

@@ -0,0 +1,35 @@
+use aoc::year2025::day08::*;
+
+const EXAMPLE: &str = "\
+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 part1_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part1_testable(&input, 10), 40);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part2(&input), 25272);
+}