Day 9: Disk Defragmenter

README.md

@@ -13,4 +13,4 @@ Development occurs in language-specific directories:
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
 |[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.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)|

rs/benches/criterion.rs

@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -62,6 +62,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day8::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(9)?;
+    let mut g = c.benchmark_group("day 9");
+    g.bench_function("part 1", |b| b.iter(|| day9::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day9::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day9.rs

@@ -0,0 +1,83 @@
+fn tri_range(offset: u64, size: u64) -> u64 {
+    (2 * offset + size - 1) * size / 2
+}
+
+pub fn part1(data: &str) -> u64 {
+    let mut sizes = data
+        .chars()
+        .filter_map(|c| c.to_digit(10))
+        .collect::<Vec<_>>();
+    let (mut total, mut offset) = (0, 0);
+    for i in 0..sizes.len() {
+        let size = sizes[i];
+        if i % 2 == 0 {
+            total += i as u64 / 2 * tri_range(offset, size.into());
+            offset += size as u64;
+        } else {
+            let mut free_size = size;
+            for (j, size) in sizes.iter_mut().enumerate().skip(i + 1).step_by(2).rev() {
+                if free_size == 0 {
+                    break;
+                }
+                let used_size = free_size.min(*size);
+                total += j as u64 / 2 * tri_range(offset, used_size.into());
+                offset += used_size as u64;
+                free_size -= used_size;
+                *size -= used_size;
+            }
+        }
+    }
+    total
+}
+
+pub fn part2(data: &str) -> u64 {
+    let mut chunks = data
+        .chars()
+        .filter_map(|c| c.to_digit(10))
+        .scan(0, |acc, size| {
+            let offset = *acc;
+            *acc = offset + size;
+            Some((offset, size))
+        })
+        .collect::<Vec<_>>();
+    (0..chunks.len())
+        .step_by(2)
+        .rev()
+        .map(|i| {
+            let (mut offset, size) = chunks[i];
+            if let Some((free_offset, free_size)) = chunks
+                .iter_mut()
+                .take(i)
+                .skip(1)
+                .step_by(2)
+                .find(|(_, free_size)| size <= *free_size)
+            {
+                offset = *free_offset;
+                *free_offset += size;
+                *free_size -= size;
+            }
+            i as u64 / 2 * tri_range(offset.into(), size.into())
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        2333133121414131402
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(1928, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(2858, part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -6,3 +6,4 @@ pub mod day5;
 pub mod day6;
 pub mod day7;
 pub mod day8;
+pub mod day9;

rs/src/main.rs

@@ -1,5 +1,5 @@
 use anyhow::anyhow;
-use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8};
+use aoc2024::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -81,5 +81,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("9") {
+        println!("Day 9");
+        let data = get_day_input(9)?;
+        println!("{:?}", day9::part1(&data));
+        println!("{:?}", day9::part2(&data));
+        println!();
+    }
+
     Ok(())
 }