Day 10: Hoof It

README.md

@@ -14,4 +14,4 @@ Development occurs in language-specific directories:
 |[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)|[day7.rs](rs/src/day7.rs)|
 |[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)|[day8.rs](rs/src/day8.rs)|
 |[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.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)|

rs/benches/criterion.rs

@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2024::{day1, day10, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -68,6 +68,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day9::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(10)?;
+    let mut g = c.benchmark_group("day 10");
+    g.bench_function("part 1", |b| b.iter(|| day10::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day10::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day10.rs

@@ -0,0 +1,100 @@
+use std::array;
+use std::collections::{BTreeMap, BTreeSet};
+
+fn parse(data: &str) -> [BTreeSet<(usize, usize)>; 10] {
+    let mut elevations = array::from_fn(|_| BTreeSet::new());
+    for (y, line) in data.lines().enumerate() {
+        for (x, c) in line.char_indices() {
+            if let Some(h) = c.to_digit(10) {
+                elevations[h as usize].insert((y, x));
+            }
+        }
+    }
+    elevations
+}
+
+fn step<T, F>(
+    acc: &BTreeMap<(usize, usize), T>,
+    points: &BTreeSet<(usize, usize)>,
+    plus: F,
+) -> BTreeMap<(usize, usize), T>
+where
+    T: Clone,
+    F: Fn(&T, &T) -> T,
+{
+    let mut ret = BTreeMap::new();
+    for ((y, x), value) in acc {
+        for (dy, dx) in [(-1, 0), (0, -1), (0, 1), (1, 0)] {
+            if let Some(point) = y
+                .checked_add_signed(dy)
+                .zip(x.checked_add_signed(dx))
+                .filter(|point| points.contains(point))
+            {
+                ret.entry(point)
+                    .and_modify(|e: &mut T| *e = plus(value, e))
+                    .or_insert_with(|| value.clone());
+            }
+        }
+    }
+    ret
+}
+
+pub fn part1(data: &str) -> usize {
+    let elevations = parse(data);
+    elevations[1..]
+        .iter()
+        .fold(
+            elevations[0]
+                .iter()
+                .map(|point| (*point, [*point].into_iter().collect()))
+                .collect(),
+            |acc, points| {
+                step(&acc, points, |x, y| -> BTreeSet<_> {
+                    x.union(y).copied().collect()
+                })
+            },
+        )
+        .values()
+        .map(|value| value.len())
+        .sum()
+}
+
+pub fn part2(data: &str) -> usize {
+    let elevations = parse(data);
+    elevations[1..]
+        .iter()
+        .fold(
+            elevations[0].iter().map(|point| (*point, 1usize)).collect(),
+            |acc, points| step(&acc, points, |x, y| x + y),
+        )
+        .values()
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        89010123
+        78121874
+        87430965
+        96549874
+        45678903
+        32019012
+        01329801
+        10456732
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(36, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(81, part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod day1;
+pub mod day10;
 pub mod day2;
 pub mod day3;
 pub mod day4;

rs/src/main.rs

@@ -1,5 +1,5 @@
 use anyhow::anyhow;
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
+use aoc2024::{day1, day10, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -89,5 +89,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("10") {
+        println!("Day 10");
+        let data = get_day_input(10)?;
+        println!("{:?}", day10::part1(&data));
+        println!("{:?}", day10::part2(&data));
+        println!();
+    }
+
     Ok(())
 }