[2025] Day 7 draft

Author: connorslade

README.md

@@ -11,6 +11,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 04: Printing Department](aoc_2025/src/day_04.rs)
 - [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)
 <!-- 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_07.rs

@@ -0,0 +1,116 @@
+use std::{
+    collections::{HashMap, HashSet},
+    convert::identity,
+};
+
+use aoc_lib::{direction::cardinal::Direction, matrix::Grid};
+use common::{Answer, solution};
+use nd_vec::vector;
+
+solution!("Laboratories", 7);
+
+fn part_a(input: &str) -> Answer {
+    let grid = Grid::parse(input, identity);
+    let start = grid.find('S').unwrap();
+
+    let mut beams = HashSet::new();
+    beams.insert(start);
+
+    let mut out = 0;
+
+    loop {
+        let mut next_beams = HashSet::new();
+        for beam in beams.iter() {
+            let next = Direction::Down.advance(*beam);
+            let Some(tile) = grid.get(next) else {
+                continue;
+            };
+
+            if *tile == '^' {
+                out += 1;
+                next_beams.insert(next - vector!(1, 0));
+                next_beams.insert(next + vector!(1, 0));
+            } else {
+                next_beams.insert(next);
+            }
+        }
+
+        if next_beams.is_empty() {
+            break;
+        }
+
+        beams = next_beams;
+    }
+
+    out.into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let grid = Grid::parse(input, identity);
+    let start = grid.find('S').unwrap();
+
+    let mut beams = HashMap::new();
+    beams.insert(start, 1_u64);
+
+    // let mut out = 0;
+
+    loop {
+        let mut next_beams = HashMap::new();
+        for (beam, count) in beams.iter() {
+            let next = Direction::Down.advance(*beam);
+            let Some(tile) = grid.get(next) else {
+                continue;
+            };
+
+            if *tile == '^' {
+                *next_beams.entry(next - vector!(1, 0)).or_default() += *count;
+                *next_beams.entry(next + vector!(1, 0)).or_default() += *count;
+            } else {
+                *next_beams.entry(next).or_default() += *count;
+            }
+        }
+
+        println!("count : {}", next_beams.len());
+        if next_beams.is_empty() {
+            break;
+        }
+
+        beams = next_beams;
+    }
+
+    beams.iter().map(|x| x.1).sum::<u64>().into()
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        .......S.......
+        ...............
+        .......^.......
+        ...............
+        ......^.^......
+        ...............
+        .....^.^.^.....
+        ...............
+        ....^.^...^....
+        ...............
+        ...^.^...^.^...
+        ...............
+        ..^...^.....^..
+        ...............
+        .^.^.^.^.^...^.
+        ...............
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 21.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 40.into());
+    }
+}

aoc_2025/src/lib.rs

@@ -6,6 +6,7 @@ mod day_03;
 mod day_04;
 mod day_05;
 mod day_06;
+mod day_07;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -15,5 +16,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_04::SOLUTION,
     day_05::SOLUTION,
     day_06::SOLUTION,
+    day_07::SOLUTION,
     // [list_marker]
 ];