Year 2025 Day 6

Author: maneatingape

README.md

@@ -82,6 +82,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 3 | [Lobby](https://adventofcode.com/2025/day/3) | [Source](src/year2025/day03.rs) | 21 |
 | 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) | 24 |
 
 ## 2024
 

benches/benchmark.rs

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

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

src/main.rs

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

src/year2025/day06.rs

@@ -0,0 +1,42 @@
+use crate::util::grid::*;
+use crate::util::point::*;
+
+pub fn parse(input: &str) -> Grid<u8> {
+    Grid::parse(input)
+}
+
+pub fn part1(grid: &Grid<u8>) -> u64 {
+    math(grid, true)
+}
+
+pub fn part2(grid: &Grid<u8>) -> u64 {
+    math(grid, false)
+}
+
+fn math(grid: &Grid<u8>, part_one: bool) -> u64 {
+    let top = grid.height - 1;
+    let mut right = grid.width;
+
+    (0..grid.width)
+        .rev()
+        .filter(|&x| grid[Point::new(x, top)] != b' ')
+        .map(|left| {
+            let plus = grid[Point::new(left, top)] == b'+';
+            let extra: u64 = if part_one {
+                let iter = (0..top).map(|y| (left..right).fold(0, |num, x| acc(grid, num, x, y)));
+                if plus { iter.sum() } else { iter.product() }
+            } else {
+                let iter = (left..right).map(|x| (0..top).fold(0, |num, y| acc(grid, num, x, y)));
+                if plus { iter.sum() } else { iter.product() }
+            };
+
+            right = left - 1;
+            extra
+        })
+        .sum()
+}
+
+fn acc(grid: &Grid<u8>, number: u64, x: i32, y: i32) -> u64 {
+    let digit = grid[Point::new(x, y)];
+    if digit == b' ' { number } else { 10 * number + (digit - b'0') as u64 }
+}

tests/test.rs

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

tests/year2025/day06.rs

@@ -0,0 +1,19 @@
+use aoc::year2025::day06::*;
+
+const EXAMPLE: &str = "\
+123 328  51 64 
+ 45 64  387 23 
+  6 98  215 314
+*   +   *   +  ";
+
+#[test]
+fn part1_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part1(&input), 4277556);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part2(&input), 3263827);
+}