Day 17: Chronospatial Computer

README.md

@@ -21,4 +21,4 @@ Development occurs in language-specific directories:
 |[Day14.hs](hs/src/Day14.hs)|[Day14.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day14.kt)|[day14.py](py/aoc2024/day14.py)|[day14.rs](rs/src/day14.rs)|
 |[Day15.hs](hs/src/Day15.hs)|[Day15.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day15.kt)|[day15.py](py/aoc2024/day15.py)|[day15.rs](rs/src/day15.rs)|
 |[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)|[day16.rs](rs/src/day16.rs)|
-|[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|[day17.py](py/aoc2024/day17.py)||
+|[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|[day17.py](py/aoc2024/day17.py)|[day17.rs](rs/src/day17.rs)|

rs/benches/criterion.rs

@@ -1,6 +1,6 @@
 use aoc2024::{
-    day1, day10, day11, day12, day13, day14, day15, day16, day2, day3, day4, day5, day6, day7,
-    day8, day9,
+    day1, day10, day11, day12, day13, day14, day15, day16, day17, day2, day3, day4, day5, day6,
+    day7, day8, day9,
 };
 use criterion::{black_box, Criterion};
 use std::env;
@@ -113,6 +113,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day16::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(17)?;
+    let mut g = c.benchmark_group("day 17");
+    g.bench_function("part 1", |b| b.iter(|| day17::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day17::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day17.rs

@@ -0,0 +1,113 @@
+use itertools::Itertools;
+
+fn parse(data: &str) -> Option<(usize, usize, usize, Vec<usize>)> {
+    let mut iter = data.lines();
+    let a = iter.next()?.strip_prefix("Register A: ")?.parse().ok()?;
+    let b = iter.next()?.strip_prefix("Register B: ")?.parse().ok()?;
+    let c = iter.next()?.strip_prefix("Register C: ")?.parse().ok()?;
+    let program = iter
+        .find(|line| !line.is_empty())?
+        .strip_prefix("Program: ")?
+        .split(',')
+        .map(|s| s.parse())
+        .collect::<Result<_, _>>()
+        .ok()?;
+    Some((a, b, c, program))
+}
+
+fn run(mut a: usize, mut b: usize, mut c: usize, program: &[usize]) -> Option<Vec<usize>> {
+    let mut outputs = vec![];
+    let mut ip = 0;
+    while let Some((instruction, operand)) = program.get(ip).zip(program.get(ip + 1)) {
+        let combo = match operand {
+            0..=3 => *operand,
+            4 => a,
+            5 => b,
+            6 => c,
+            _ => return None,
+        };
+        match instruction {
+            0 => a >>= combo,
+            1 => b ^= operand,
+            2 => b = combo & 7,
+            3 => {
+                if a != 0 {
+                    ip = *operand;
+                    continue;
+                }
+            }
+            4 => b ^= c,
+            5 => outputs.push(combo & 7),
+            6 => b = a >> combo,
+            7 => c = a >> combo,
+            _ => return None,
+        }
+        ip += 2;
+    }
+    Some(outputs)
+}
+
+pub fn part1(data: &str) -> Option<String> {
+    let (a, b, c, program) = parse(data)?;
+    Some(
+        run(a, b, c, &program)?
+            .into_iter()
+            .map(|num| num.to_string())
+            .join(","),
+    )
+}
+
+pub fn part2(data: &str) -> Option<usize> {
+    let (_, b, c, program) = parse(data)?;
+    let mut candidates = vec![0];
+    while !candidates.is_empty() {
+        let mut next = vec![];
+        for base in candidates {
+            for i in 0..=7 {
+                let a = 8 * base + i;
+                let output = run(a, b, c, &program)?;
+                if output == program {
+                    return Some(a);
+                }
+                if program.ends_with(&output) {
+                    next.push(a);
+                }
+            }
+        }
+        candidates = next;
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE_1: &str = indoc! {"
+        Register A: 729
+        Register B: 0
+        Register C: 0
+
+        Program: 0,1,5,4,3,0
+    "};
+
+    static EXAMPLE_2: &str = indoc! {"
+        Register A: 2024
+        Register B: 0
+        Register C: 0
+
+        Program: 0,3,5,4,3,0
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(Some("4,6,3,5,6,3,5,2,1,0".to_string()), part1(EXAMPLE_1));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(Some(117440), part2(EXAMPLE_2));
+    }
+}

rs/src/lib.rs

@@ -6,6 +6,7 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day16;
+pub mod day17;
 pub mod day2;
 pub mod day3;
 pub mod day4;

rs/src/main.rs

@@ -1,7 +1,7 @@
 use anyhow::anyhow;
 use aoc2024::{
-    day1, day10, day11, day12, day13, day14, day15, day16, day2, day3, day4, day5, day6, day7,
-    day8, day9,
+    day1, day10, day11, day12, day13, day14, day15, day16, day17, day2, day3, day4, day5, day6,
+    day7, day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -148,5 +148,13 @@ fn main() -> anyhow::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("17") {
+        println!("Day 17");
+        let data = get_day_input(17)?;
+        println!("{}", day17::part1(&data).ok_or(anyhow!("None"))?);
+        println!("{:?}", day17::part2(&data).ok_or(anyhow!("None"))?);
+        println!();
+    }
+
     Ok(())
 }