Year 2025 Day 12

Author: maneatingape

README.md

@@ -88,6 +88,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 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) | 75 |
+| 12 | [Christmas Tree Farm](https://adventofcode.com/2025/day/12) | [Source](src/year2025/day12.rs) | 22 |
 
 ## 2024
 

benches/benchmark.rs

@@ -95,5 +95,5 @@ benchmark!(year2024
 );
 
 benchmark!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12
 );

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, day11
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12
 );

src/main.rs

@@ -141,5 +141,5 @@ run!(year2024
 );
 
 run!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12
 );

src/year2025/day12.rs

@@ -0,0 +1,27 @@
+//! # Christmas Tree Farm
+use crate::util::iter::*;
+use crate::util::parse::*;
+
+pub fn parse(input: &str) -> &str {
+    input
+}
+
+pub fn part1(input: &str) -> usize {
+    let blocks: Vec<_> = input.split("\n\n").collect();
+    let sizes: Vec<_> =
+        blocks[..6].iter().map(|block| block.bytes().filter(|&b| b == b'#').count()).collect();
+
+    blocks[6]
+        .iter_unsigned::<usize>()
+        .chunk::<8>()
+        .filter(|region| {
+            let area = region[0] * region[1];
+            let needed: usize = sizes.iter().zip(&region[2..]).map(|(x, y)| x * y).sum();
+            needed <= area
+        })
+        .count()
+}
+
+pub fn part2(_input: &str) -> &'static str {
+    "n/a"
+}

tests/test.rs

@@ -87,5 +87,5 @@ test!(year2024
 );
 
 test!(year2025
-    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11
+    day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12
 );

tests/year2025/day12.rs

@@ -0,0 +1,9 @@
+#[test]
+fn part1_test() {
+    // Specific to real actual input.
+}
+
+#[test]
+fn part2_test() {
+    // Not applicable.
+}