Year 2025 Day 7

Author: maneatingape

README.md

@@ -83,6 +83,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 4 | [Printing Department](https://adventofcode.com/2025/day/4) | [Source](src/year2025/day04.rs) | 177 |
 | 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) | 15 |
 
 ## 2024
 

benches/benchmark.rs

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

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
+    day01, day02, day03, day04, day05, day06, day07
 );

src/main.rs

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

src/year2025/day07.rs

@@ -0,0 +1,46 @@
+//! # Laboratories
+type Input = (u64, u64);
+
+pub fn parse(input: &str) -> Input {
+    let lines: Vec<_> = input.lines().map(str::as_bytes).collect();
+    let width = lines[0].len();
+    let start = lines[0].iter().position(|&b| b == b'S').unwrap();
+
+    let mut splits = 0;
+    let mut current = vec![0; width];
+    let mut next = vec![0; width];
+
+    current[start] = 1;
+
+    for &row in &lines[1..] {
+        for (x, &count) in current.iter().enumerate() {
+            if count > 0 {
+                if row[x] == b'^' {
+                    splits += 1;
+
+                    if x > 0 {
+                        next[x - 1] += count;
+                    }
+                    if x + 1 < width {
+                        next[x + 1] += count;
+                    }
+                } else {
+                    next[x] += count;
+                }
+            }
+        }
+
+        (current, next) = (next, current);
+        next.fill(0);
+    }
+
+    (splits, current.iter().sum())
+}
+
+pub fn part1(input: &Input) -> u64 {
+    input.0
+}
+
+pub fn part2(input: &Input) -> u64 {
+    input.1
+}

tests/test.rs

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

tests/year2025/day07.rs

@@ -0,0 +1,31 @@
+use aoc::year2025::day07::*;
+
+const EXAMPLE: &str = "\
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............";
+
+#[test]
+fn part1_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part1(&input), 21);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part2(&input), 40);
+}