Day 12: Garden Groups

ephemient · Dec 17, 2024 · f5fd3a3 · f5fd3a3
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diff --git a/README.md b/README.md
@@ -16,7 +16,7 @@ Development occurs in language-specific directories:
 |[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day9.kt)|[day9.py](py/aoc2024/day9.py)|[day9.rs](rs/src/day9.rs)|
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt)|[day10.py](py/aoc2024/day10.py)|[day10.rs](rs/src/day10.rs)|
 |[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt)|[day11.py](py/aoc2024/day11.py)|[day11.rs](rs/src/day11.rs)|
-|[Day12.hs](hs/src/Day12.hs)|[Day12.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day12.kt)|[day12.py](py/aoc2024/day12.py)||
+|[Day12.hs](hs/src/Day12.hs)|[Day12.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day12.kt)|[day12.py](py/aoc2024/day12.py)|[day12.rs](rs/src/day12.rs)|
 |[Day13.hs](hs/src/Day13.hs)|[Day13.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day13.kt)|[day13.py](py/aoc2024/day13.py)||
 |[Day14.hs](hs/src/Day14.hs)|[Day14.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day14.kt)|||
 |[Day15.hs](hs/src/Day15.hs)||||

diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2024::{day1, day10, day11, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2024::{day1, day10, day11, day12, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -80,6 +80,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day11::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(12)?;
+    let mut g = c.benchmark_group("day 12");
+    g.bench_function("part 1", |b| b.iter(|| day12::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day12::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

diff --git a/rs/src/day12.rs b/rs/src/day12.rs
@@ -0,0 +1,173 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+use if_chain::if_chain;
+use itertools::Itertools;
+
+struct Data<'a> {
+    lines: Vec<&'a str>,
+}
+
+impl Data<'_> {
+    fn new(data: &str) -> Data {
+        Data {
+            lines: data.lines().collect(),
+        }
+    }
+
+    fn groups(&self) -> impl Iterator<Item = BTreeSet<(usize, usize)>> + use<'_> {
+        self.lines
+            .iter()
+            .enumerate()
+            .flat_map(|(y, line)| line.bytes().enumerate().map(move |(x, b)| ((y, x), b)))
+            .scan(BTreeSet::new(), |visited, (pos, b)| {
+                if !visited.insert(pos) {
+                    return Some(None);
+                }
+                let mut group = BTreeSet::new();
+                let mut stack = vec![pos];
+                while let Some(pos @ (y, x)) = stack.pop() {
+                    group.insert(pos);
+                    for (dy, dx) in [(-1, 0), (0, -1), (0, 1), (1, 0)] {
+                        if_chain! {
+                            if let Some(y) = y.checked_add_signed(dy);
+                            if let Some(line) = self.lines.get(y);
+                            if let Some(x) = x.checked_add_signed(dx);
+                            if line.as_bytes().get(x).copied() == Some(b);
+                            if visited.insert((y, x));
+                            then {
+                                stack.push((y, x));
+                            }
+                        }
+                    }
+                }
+                Some(Some(group))
+            })
+            .flatten()
+    }
+}
+
+fn perimeter1(group: &BTreeSet<(usize, usize)>) -> usize {
+    let mut edges = BTreeMap::<_, u8>::new();
+    for (y, x) in group.iter() {
+        for edge in [
+            (2 * y, 2 * x + 1),
+            (2 * y + 1, 2 * x),
+            (2 * y + 1, 2 * x + 2),
+            (2 * y + 2, 2 * x + 1),
+        ] {
+            *edges.entry(edge).or_default() += 1;
+        }
+    }
+    edges.into_values().filter(|value| *value == 1).count()
+}
+
+pub fn part1(data: &str) -> usize {
+    Data::new(data)
+        .groups()
+        .map(|group| group.len() * perimeter1(&group))
+        .sum()
+}
+
+fn perimeter2(group: &BTreeSet<(usize, usize)>) -> usize {
+    let mut edges = BTreeMap::<_, u8>::new();
+    for (y, x) in group.iter() {
+        *edges.entry((2 * y, 2 * x + 1)).or_default() |= 1;
+        *edges.entry((2 * y + 1, 2 * x)).or_default() |= 2;
+        *edges.entry((2 * y + 1, 2 * x + 2)).or_default() |= 8;
+        *edges.entry((2 * y + 2, 2 * x + 1)).or_default() |= 4;
+    }
+    let mut lines = BTreeMap::<_, BTreeSet<_>>::new();
+    for ((y, x), n) in edges {
+        if n & (n - 1) == 0 {
+            lines
+                .entry(if n.ilog2() % 2 == 0 { y + 1 } else { x })
+                .or_default()
+                .insert((x + y, n));
+        }
+    }
+    lines
+        .into_values()
+        .map(|line| {
+            line.into_iter()
+                .tuple_windows()
+                .filter(|((p, b), (q, d))| p.abs_diff(*q) > 2 || b != d)
+                .count()
+                + 1
+        })
+        .sum()
+}
+
+pub fn part2(data: &str) -> usize {
+    Data::new(data)
+        .groups()
+        .map(|group| group.len() * perimeter2(&group))
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE_1: &str = indoc! {"
+        AAAA
+        BBCD
+        BBCC
+        EEEC
+    "};
+
+    static EXAMPLE_2: &str = indoc! {"
+        OOOOO
+        OXOXO
+        OOOOO
+        OXOXO
+        OOOOO
+    "};
+
+    static EXAMPLE_3: &str = indoc! {"
+        RRRRIICCFF
+        RRRRIICCCF
+        VVRRRCCFFF
+        VVRCCCJFFF
+        VVVVCJJCFE
+        VVIVCCJJEE
+        VVIIICJJEE
+        MIIIIIJJEE
+        MIIISIJEEE
+        MMMISSJEEE
+    "};
+
+    static EXAMPLE_4: &str = indoc! {"
+        EEEEE
+        EXXXX
+        EEEEE
+        EXXXX
+        EEEEE
+    "};
+
+    static EXAMPLE_5: &str = indoc! {"
+        AAAAAA
+        AAABBA
+        AAABBA
+        ABBAAA
+        ABBAAA
+        AAAAAA
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(140, part1(EXAMPLE_1));
+        assert_eq!(772, part1(EXAMPLE_2));
+        assert_eq!(1930, part1(EXAMPLE_3));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(80, part2(EXAMPLE_1));
+        assert_eq!(436, part2(EXAMPLE_2));
+        assert_eq!(236, part2(EXAMPLE_4));
+        assert_eq!(368, part2(EXAMPLE_5));
+        assert_eq!(1206, part2(EXAMPLE_3));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
@@ -1,6 +1,7 @@
 pub mod day1;
 pub mod day10;
 pub mod day11;
+pub mod day12;
 pub mod day2;
 pub mod day3;
 pub mod day4;

diff --git a/rs/src/main.rs b/rs/src/main.rs
@@ -1,5 +1,5 @@
 use anyhow::anyhow;
-use aoc2024::{day1, day10, day11, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2024::{day1, day10, day11, day12, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -105,5 +105,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("12") {
+        println!("Day 12");
+        let data = get_day_input(12)?;
+        println!("{:?}", day12::part1(&data));
+        println!("{:?}", day12::part2(&data));
+        println!();
+    }
+
     Ok(())
 }