[2025] Day 11 draft

Author: connorslade

README.md

@@ -15,6 +15,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 08: Playground](aoc_2025/src/day_08.rs)
 - [Day 09: Movie Theater](aoc_2025/src/day_09.rs)
 - [Day 10: Factory](aoc_2025/src/day_10.rs)
+- [Day 11: Reactor](aoc_2025/src/day_11.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_11.rs

@@ -0,0 +1,110 @@
+use std::collections::HashMap;
+
+use common::{Answer, solution};
+
+solution!("Reactor", 11);
+
+fn part_a(input: &str) -> Answer {
+    let mut map = HashMap::new();
+
+    for line in input.lines() {
+        let (from, to) = line.split_once(": ").unwrap();
+        let to = to.split_whitespace().collect::<Vec<_>>();
+        map.insert(from, to);
+    }
+
+    fn count_paths(map: &HashMap<&str, Vec<&str>>, current: &str) -> u64 {
+        if current == "out" {
+            return 1;
+        }
+
+        let mut out = 0;
+
+        for child in &map[current] {
+            out += count_paths(map, child);
+        }
+
+        out
+    }
+
+    count_paths(&map, "you").into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let mut map = HashMap::new();
+
+    for line in input.lines() {
+        let (from, to) = line.split_once(": ").unwrap();
+        let to = to.split_whitespace().collect::<Vec<_>>();
+        map.insert(from, to);
+    }
+
+    fn count_paths<'a>(
+        memo: &mut HashMap<(&'a str, bool, bool), u64>,
+        map: &HashMap<&str, Vec<&'a str>>,
+        current: &'a str,
+        mut fft: bool,
+        mut dac: bool,
+    ) -> u64 {
+        let key = (current, fft, dac);
+        if let Some(memo) = memo.get(&key) {
+            return *memo;
+        }
+
+        if current == "out" {
+            if fft && dac {
+                return 1;
+            }
+            return 0;
+        }
+
+        if current == "fft" {
+            fft = true;
+        }
+
+        if current == "dac" {
+            dac = true;
+        }
+
+        let mut out = 0;
+        for child in &map[current] {
+            out += count_paths(memo, map, child, fft, dac);
+        }
+
+        memo.insert(key, out);
+        out
+    }
+
+    count_paths(&mut HashMap::new(), &map, "svr", false, false).into()
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        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 part_a() {
+        assert_eq!(super::part_a(CASE), 5.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 2.into());
+    }
+}

aoc_2025/src/lib.rs

@@ -10,6 +10,7 @@ mod day_07;
 mod day_08;
 mod day_09;
 mod day_10;
+mod day_11;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -23,5 +24,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_08::SOLUTION,
     day_09::SOLUTION,
     day_10::SOLUTION,
+    day_11::SOLUTION,
     // [list_marker]
 ];