Year 2024 Day 17

Author: maneatingape

README.md

@@ -88,6 +88,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 14 | [Restroom Redoubt](https://adventofcode.com/2024/day/14) | [Source](src/year2024/day14.rs) | 74 |
 | 15 | [Warehouse Woes](https://adventofcode.com/2024/day/15) | [Source](src/year2024/day15.rs) | 303 |
 | 16 | [Reindeer Maze](https://adventofcode.com/2024/day/16) | [Source](src/year2024/day16.rs) | 422 |
+| 17 | [Chronospatial Computer](https://adventofcode.com/2024/day/17) | [Source](src/year2024/day17.rs) | 7 |
 
 ## 2023
 

benches/benchmark.rs

@@ -88,5 +88,5 @@ benchmark!(year2023
 
 benchmark!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16
+    day14, day15, day16, day17
 );

src/lib.rs

@@ -68,5 +68,5 @@ library!(year2023 "Restore global snow production."
 
 library!(year2024 "Locate the Chief Historian in time for the big Christmas sleigh launch."
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16
+    day14, day15, day16, day17
 );

src/main.rs

@@ -142,5 +142,5 @@ run!(year2023
 
 run!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16
+    day14, day15, day16, day17
 );

src/year2024/day17.rs

@@ -0,0 +1,94 @@
+//! # Chronospatial Computer
+use crate::util::parse::*;
+
+pub fn parse(input: &str) -> Vec<u64> {
+    input.iter_unsigned::<u64>().collect()
+}
+
+pub fn part1(input: &[u64]) -> String {
+    let mut computer =
+        Computer { program: &input[3..], ip: 0, a: input[0], b: input[1], c: input[2] };
+    let mut out = Vec::new();
+
+    while let Some(n) = computer.run() {
+        let digit = (n as u8 + b'0') as char;
+        out.push(digit);
+        out.push(',');
+    }
+
+    out.pop();
+    out.iter().collect()
+}
+
+pub fn part2(input: &[u64]) -> u64 {
+    let mut valid = vec![0];
+
+    for &out in input.iter().skip(3).rev() {
+        let mut next = Vec::new();
+
+        for v in valid {
+            for n in 0..8 {
+                let a = (v << 3) | n;
+                let mut computer =
+                    Computer { program: &input[3..], ip: 0, a, b: input[1], c: input[2] };
+
+                if let Some(result) = computer.run() {
+                    if result == out {
+                        next.push(a);
+                    }
+                }
+            }
+        }
+
+        valid = next;
+    }
+
+    *valid.iter().min().unwrap()
+}
+
+struct Computer<'a> {
+    program: &'a [u64],
+    ip: usize,
+    a: u64,
+    b: u64,
+    c: u64,
+}
+
+impl Computer<'_> {
+    fn run(&mut self) -> Option<u64> {
+        while self.ip < self.program.len() {
+            let combo = |index| match self.program[index] {
+                0..4 => self.program[index],
+                4 => self.a,
+                5 => self.b,
+                6 => self.c,
+                _ => unreachable!(),
+            };
+
+            match self.program[self.ip] {
+                0 => self.a >>= combo(self.ip + 1),
+                1 => self.b ^= self.program[self.ip + 1],
+                2 => self.b = combo(self.ip + 1) % 8,
+                3 => {
+                    if self.a != 0 {
+                        self.ip = self.program[self.ip + 1] as usize;
+                        continue;
+                    }
+                }
+                4 => self.b ^= self.c,
+                5 => {
+                    let out = combo(self.ip + 1) % 8;
+                    self.ip += 2;
+                    return Some(out);
+                }
+                6 => self.b = self.a >> combo(self.ip + 1),
+                7 => self.c = self.a >> combo(self.ip + 1),
+                _ => unreachable!(),
+            }
+
+            self.ip += 2;
+        }
+
+        None
+    }
+}

tests/test.rs

@@ -81,5 +81,5 @@ test!(year2023
 
 test!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16
+    day14, day15, day16, day17
 );

tests/year2024/day17.rs

@@ -0,0 +1,27 @@
+use aoc::year2024::day17::*;
+
+const FIRST_EXAMPLE: &str = "\
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,1,5,4,3,0";
+
+const SECOND_EXAMPLE: &str = "\
+Register A: 2024
+Register B: 0
+Register C: 0
+
+Program: 0,3,5,4,3,0";
+
+#[test]
+fn part1_test() {
+    let input = parse(FIRST_EXAMPLE);
+    assert_eq!(part1(&input), "4,6,3,5,6,3,5,2,1,0");
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(SECOND_EXAMPLE);
+    assert_eq!(part2(&input), 117440);
+}