Year 2025 Day 11

Author: maneatingape

README.md

@@ -87,6 +87,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 8 | [Playground](https://adventofcode.com/2025/day/8) | [Source](src/year2025/day08.rs) | 527 |
 | 9 | [Movie Theater](https://adventofcode.com/2025/day/9) | [Source](src/year2025/day09.rs) | 668 |
 | 10 | [Factory](https://adventofcode.com/2025/day/10) | [Source](src/year2025/day10.rs) | 117* |
+| 11 | [Reactor](https://adventofcode.com/2025/day/11) | [Source](src/year2025/day11.rs) | 100 |
 
 ## 2024
 

benches/benchmark.rs

@@ -95,5 +95,5 @@ benchmark!(year2024
 );
 
 benchmark!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
 );

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, day08, day09, day10
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
 );

src/main.rs

@@ -141,5 +141,5 @@ run!(year2024
 );
 
 run!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
 );

src/year2025/day11.rs

@@ -0,0 +1,54 @@
+//! # Reactor
+use crate::util::hash::*;
+
+pub struct Input<'a> {
+    indices: FastMap<&'a str, usize>,
+    graph: Vec<Vec<usize>>,
+}
+
+pub fn parse(input: &str) -> Input<'_> {
+    let nodes: Vec<Vec<_>> =
+        input.lines().map(|line| line.split_ascii_whitespace().collect()).collect();
+    let mut indices = FastMap::new();
+
+    for label in nodes.iter().flatten() {
+        let size = indices.len();
+        indices.entry(&label[..3]).or_insert(size);
+    }
+
+    let mut graph = vec![vec![]; indices.len()];
+
+    for edges in nodes {
+        let from = indices[&edges[0][..3]];
+        graph[from].extend(edges[1..].iter().map(|label| indices[label]));
+    }
+
+    Input { indices, graph }
+}
+
+pub fn part1(input: &Input<'_>) -> u64 {
+    paths(input, "you", "out")
+}
+
+pub fn part2(input: &Input<'_>) -> u64 {
+    let one = paths(input, "svr", "fft") * paths(input, "fft", "dac") * paths(input, "dac", "out");
+    let two = paths(input, "svr", "dac") * paths(input, "dac", "fft") * paths(input, "fft", "out");
+    one + two
+}
+
+fn paths(input: &Input<'_>, from: &str, to: &str) -> u64 {
+    let mut cache = vec![u64::MAX; input.indices.len()];
+    dfs(input, &mut cache, input.indices[from], input.indices[to])
+}
+
+fn dfs(input: &Input<'_>, cache: &mut [u64], node: usize, end: usize) -> u64 {
+    if node == end {
+        1
+    } else if cache[node] == u64::MAX {
+        let result = input.graph[node].iter().map(|&next| dfs(input, cache, next, end)).sum();
+        cache[node] = result;
+        result
+    } else {
+        cache[node]
+    }
+}

tests/test.rs

@@ -87,5 +87,5 @@ test!(year2024
 );
 
 test!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
 );

tests/year2025/day11.rs

@@ -0,0 +1,40 @@
+use aoc::year2025::day11::*;
+
+const EXAMPLE_ONE: &str = "\
+aaa: you hhh
+you: bbb ccc
+bbb: ddd eee
+ccc: ddd eee fff
+ddd: ggg
+eee: out
+fff: out
+ggg: out
+hhh: ccc fff iii
+iii: out";
+
+const EXAMPLE_TWO: &str = "\
+svr: aaa bbb
+aaa: fft
+fft: ccc
+bbb: tty
+tty: ccc
+ccc: ddd eee
+ddd: hub
+hub: fff
+eee: dac
+dac: fff
+fff: ggg hhh
+ggg: out
+hhh: out";
+
+#[test]
+fn part1_test() {
+    let input = parse(EXAMPLE_ONE);
+    assert_eq!(part1(&input), 5);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE_TWO);
+    assert_eq!(part2(&input), 2);
+}