day17: initial impl

benches/bench_today.rs

@@ -1,16 +1,16 @@
-use aoc_2024::day16::{part1, part2};
+use aoc_2024::day17::{part1, part2};
 use criterion::{criterion_group, criterion_main, Criterion};
 use std::hint::black_box;
 
 fn bench_part1(c: &mut Criterion) {
-    let input = include_str!("../input/day16.txt");
-    c.bench_function("day16_part1", |b| b.iter(|| part1(black_box(input))));
+    let input = include_str!("../input/day17.txt");
+    c.bench_function("day17_part1", |b| b.iter(|| part1(black_box(input))));
 }
 
 fn bench_part2(c: &mut Criterion) {
-    let input = include_str!("../input/day16.txt");
-    c.bench_function("day16_part2", |b| b.iter(|| part2(black_box(input))));
+    let input = include_str!("../input/day17.txt");
+    c.bench_function("day17_part2", |b| b.iter(|| part2(black_box(input))));
 }
 
-criterion_group!(benches, bench_part1, bench_part2,);
+criterion_group!(benches, bench_part1, bench_part2);
 criterion_main!(benches);

src/day17.rs

@@ -0,0 +1,122 @@
+#![expect(static_mut_refs, clippy::cast_possible_truncation)]
+
+use std::hint::unreachable_unchecked;
+
+pub fn part1(input: &str) -> &'static str {
+    unsafe { part1_inner(input.as_bytes()) }
+}
+
+unsafe fn parse(mut input: &[u8]) -> (u64, &[u8]) {
+    input = input.get_unchecked(12..);
+
+    let mut a = 0;
+    while *input.get_unchecked(0) != b'\n' {
+        a = a * 10 + (*input.get_unchecked(0) - b'0') as u64;
+        input = input.get_unchecked(1..);
+    }
+
+    let program = input.get_unchecked(1 + 38..);
+    (a, program)
+}
+
+unsafe fn part1_inner(input: &[u8]) -> &'static str {
+    static mut OUTPUT: [u8; 64] = [b','; 64];
+
+    let (mut a, program) = parse(input);
+    let (mut b, mut c, mut instruction_ptr) = (0, 0, 0);
+
+    let mut output_index = 0;
+    macro_rules! push_output {
+        ($combo: expr) => {{
+            *OUTPUT.get_unchecked_mut(output_index) = ($combo) as u8 + b'0';
+            output_index += 2;
+        }};
+    }
+
+    while instruction_ptr < program.len() {
+        let literal = || (*program.get_unchecked(instruction_ptr + 2) - b'0') as u64;
+        let combo = || match literal() {
+            n @ 0..=3 => n,
+            4 => a,
+            5 => b,
+            6 => c,
+            _ => unreachable_unchecked(),
+        };
+
+        match *program.get_unchecked(instruction_ptr) {
+            b'0' => a >>= combo(),
+            b'1' => b ^= literal(),
+            b'2' => b = combo() & 7,
+            b'3' if a != 0 => instruction_ptr = (literal() * 2).wrapping_sub(4) as usize,
+            b'3' => {}
+            b'4' => b ^= c,
+            b'5' => push_output!(combo() & 7),
+            b'7' => c = a >> combo(),
+            _ => unreachable_unchecked(),
+        }
+
+        instruction_ptr = instruction_ptr.wrapping_add(4);
+    }
+    std::str::from_utf8_unchecked(OUTPUT.get_unchecked(..output_index - 1))
+}
+
+#[test]
+fn test_part1() {
+    assert_eq!(part1(include_str!("../input/day17.txt")), "7,3,5,7,5,7,4,3,0");
+}
+
+#[test]
+fn test_part2() {
+    assert_eq!(part2(include_str!("../input/day17.txt")), 105_734_774_294_938);
+}
+
+pub fn part2(input: &str) -> u64 {
+    unsafe { part2_inner(input.as_bytes()) }
+}
+
+unsafe fn part2_inner(input: &[u8]) -> u64 {
+    let (_, program) = unsafe { parse(input) };
+    recurse(program, program.len() - 2, 0).unwrap_unchecked()
+}
+
+unsafe fn recurse(program: &[u8], index: usize, mut a: u64) -> Option<u64> {
+    for _ in 0..8 {
+        if run(program, a) == (*program.get_unchecked(index) - b'0') as u64 {
+            let Some(index) = index.checked_sub(2) else { return Some(a) };
+            if let Some(a) = recurse(program, index, a << 3) {
+                return Some(a);
+            }
+        }
+        a += 1;
+    }
+    None
+}
+
+unsafe fn run(program: &[u8], mut a: u64) -> u64 {
+    let (mut b, mut c, mut instruction_ptr) = (0, 0, 0);
+    while instruction_ptr < program.len() {
+        let literal = || (*program.get_unchecked(instruction_ptr + 2) - b'0') as u64;
+        let combo = || match literal() {
+            n @ 0..=3 => n,
+            4 => a,
+            5 => b,
+            6 => c,
+            _ => unreachable_unchecked(),
+        };
+
+        match *program.get_unchecked(instruction_ptr) {
+            b'0' => a >>= combo(),
+            b'1' => b ^= literal(),
+            b'2' => b = combo() % 8,
+            b'3' if a != 0 => instruction_ptr = (literal() * 2).wrapping_sub(4) as usize,
+            b'3' => {}
+            b'4' => b ^= c,
+            b'5' => return combo() % 8,
+            b'7' => c = a >> combo(),
+            _ => unreachable_unchecked(),
+        }
+
+        instruction_ptr = instruction_ptr.wrapping_add(4);
+    }
+    unreachable_unchecked()
+}

src/lib.rs

@@ -1,6 +1,7 @@
 #![feature(array_windows)]
 #![feature(portable_simd)]
 #![feature(iter_array_chunks)]
+
 pub mod day1;
 pub mod day10;
 pub mod day11;
@@ -9,6 +10,7 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day16;
+pub mod day17;
 pub mod day2;
 pub mod day3;
 pub mod day4;