day12

src/day12.rs

@@ -0,0 +1,105 @@
+#[aoc(day12, part1)]
+pub fn part1(input: &str) -> u32 {
+    let (presents, under_trees) = parse(input);
+    under_trees
+        .iter()
+        .map(|ut| {
+            ((ut.presents
+                .iter()
+                .zip(presents.clone())
+                .map(|(num, shape)| num * shape.iter().sum::<u32>())
+                .sum::<u32>()
+                < (ut.width * ut.height))
+                && (ut.width * ut.height >= ut.presents.iter().sum::<u32>() * 9)) as u32
+        })
+        .sum()
+}
+
+type Present = Vec<u32>;
+
+#[derive(Debug)]
+struct UnderTree {
+    width: u32,
+    height: u32,
+    presents: Vec<u32>,
+}
+
+fn parse_under_tree(line: &str) -> UnderTree {
+    let mut splits = line.split(&['x', ':']);
+    let width = splits.next().unwrap().parse::<u32>().unwrap();
+    let height = splits.next().unwrap().parse::<u32>().unwrap();
+    let presents = splits
+        .next()
+        .unwrap()
+        .split_ascii_whitespace()
+        .map(|x| x.parse::<u32>().unwrap())
+        .collect();
+    UnderTree {
+        width: width,
+        height: height,
+        presents: presents,
+    }
+}
+
+fn parse(input: &str) -> (Vec<Present>, Vec<UnderTree>) {
+    (
+        input
+            .lines()
+            .filter(|l| !l.chars().next().unwrap_or('a').is_digit(10))
+            .map(|l| l.chars().map(|x| (x == '#') as u32).collect::<Vec<u32>>())
+            .collect(),
+        input
+            .rsplit_once("\n\n")
+            .unwrap()
+            .1
+            .lines()
+            .map(|l| parse_under_tree(l))
+            .collect(),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT_EXAMPLE: &str = "\
+0:
+###
+##.
+##.
+
+1:
+###
+##.
+.##
+
+2:
+.##
+###
+##.
+
+3:
+##.
+###
+##.
+
+4:
+###
+#..
+###
+
+5:
+###
+.#.
+###
+
+4x4: 0 0 0 0 2 0
+12x5: 1 0 1 0 2 2
+12x5: 1 0 1 0 3 2
+";
+
+    #[test]
+    fn test_part1() {
+        assert_eq!(part1(INPUT_EXAMPLE), 2);
+    }
+}

src/lib.rs

@@ -7,12 +7,13 @@ pub mod day1;
 pub mod day2;
 // pub mod day10;
 pub mod day11;
+pub mod day12;
 pub mod day3;
 pub mod day4;
 pub mod day5;
 pub mod day6;
 pub mod day7;
 pub mod day8;
-// pub mod day9;
+pub mod day9;
 
 aoc_lib! { year = 2025 }