Day 17
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Quentin Boyer
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248
src/bin/day17.rs
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248
src/bin/day17.rs
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use std::time::Instant;
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use aoc_2024::{load, print_res};
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use bstr::BString;
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use color_eyre::eyre::{bail, Context, OptionExt};
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use itertools::Itertools;
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#[derive(Debug, Clone, Copy)]
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pub struct Computer {
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a: u64,
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b: u64,
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c: u64,
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pc: usize,
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}
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type Parsed = (Computer, Vec<u8>);
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#[inline(never)]
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pub fn parsing(input: &BString) -> color_eyre::Result<Parsed> {
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let Some((regs, program)) = std::str::from_utf8(input)?.split_once("\n\n") else {
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bail!("Malformed input")
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};
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let mut regs = regs.lines();
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let mut extract_reg = |name: char| -> color_eyre::Result<u64> {
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regs.next()
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.ok_or_eyre("Missing register")?
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.strip_prefix("Register ")
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.ok_or_eyre("Malformed prefix")?
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.strip_prefix(name)
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.ok_or_eyre("Malformed name")?
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.strip_prefix(": ")
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.ok_or_eyre("Malformed suffix")?
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.parse()
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.map_err(Into::into)
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};
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let program = program
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.strip_prefix("Program: ")
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.ok_or_eyre("Malformed program")?
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.trim();
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Ok((
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Computer {
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a: extract_reg('A').with_context(|| "Parsing A")?,
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b: extract_reg('B').with_context(|| "Parsing B")?,
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c: extract_reg('C').with_context(|| "Parsing C")?,
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pc: 0,
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},
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program
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.split(',')
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.map(|n| {
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color_eyre::eyre::ensure!(
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n.len() == 1 && (b'0'..=b'7').contains(&n.as_bytes()[0]),
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"Instruction: {n}"
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);
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Ok(n.as_bytes()[0] - b'0')
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})
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.collect::<Result<_, _>>()?,
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))
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}
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impl Computer {
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fn combo(&self, v: u8) -> u64 {
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match v {
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0..=3 => v as u64,
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4 => self.a,
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5 => self.b,
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6 => self.c,
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invalid => unreachable!("Invalid combo: {invalid}"),
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}
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}
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pub fn run(&mut self, code: &[u8]) -> Vec<u8> {
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let mut output = Vec::new();
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while self.pc < code.len() {
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let operand = code[self.pc + 1];
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match code[self.pc] {
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// adv
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0 => {
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self.a >>= self.combo(operand);
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}
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// bxl
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1 => {
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self.b ^= operand as u64;
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}
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// bst
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2 => {
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self.b = self.combo(operand) % 8;
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}
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// jnz
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3 => {
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if self.a != 0 {
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self.pc = operand as usize;
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continue;
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}
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}
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// bxc
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4 => {
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self.b ^= self.c;
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}
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// out
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5 => {
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output.push((self.combo(operand) % 8) as u8);
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}
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// bdv
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6 => {
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self.b = self.a >> self.combo(operand);
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}
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// cdv
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7 => {
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self.c = self.a >> self.combo(operand);
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}
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invalid => unreachable!("Invalid opcode: {invalid}"),
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}
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self.pc += 2;
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}
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output
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}
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}
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#[inline(never)]
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pub fn part1((mut computer, code): Parsed) {
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print_res!(
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"Result: {}",
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computer.run(&code).iter().map(|s| s.to_string()).join(",")
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);
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}
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fn display_code(code: &[u8]) {
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fn combo_display(v: u8) {
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match v {
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0..=3 => print!("{v}"),
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4 => print!("A"),
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5 => print!("B"),
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6 => print!("C"),
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_ => print!("<INVALID>"),
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}
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}
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println!("Program:");
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for (i, chunk) in code.chunks_exact(2).enumerate() {
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print!(" [{:2}] ", i * 2);
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match chunk[0] {
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0 => {
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print!("A >>= ");
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combo_display(chunk[1]);
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}
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1 => {
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print!("B ^= {}", chunk[1]);
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}
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2 => {
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print!("B = ");
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combo_display(chunk[1]);
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print!(" % 8");
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}
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3 => {
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print!("A != 0 goto {}", chunk[1]);
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}
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4 => {
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print!("B ^= C");
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}
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5 => {
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print!("out(");
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combo_display(chunk[1]);
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print!(")");
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}
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6 => {
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print!("B = A >> ");
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combo_display(chunk[1]);
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}
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7 => {
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print!("C = A >> ");
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combo_display(chunk[1]);
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}
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_ => {
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print!("<INVALID>")
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}
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}
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println!()
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}
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}
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#[inline(never)]
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pub fn part2((computer, code): Parsed) {
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display_code(&code);
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let mut possibles = vec![0u64];
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for i in 0..code.len() {
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let mut new = Vec::new();
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for a in possibles {
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for x in 0..=7 {
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let tentative = a | x << (i * 3);
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let mut computer = computer;
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computer.a = tentative;
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let result = computer.run(&code);
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if i > 3 && (result.len() < i - 3 || result[0..(i - 3)] != code[0..(i - 3)]) {
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continue;
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}
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new.push(tentative);
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}
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}
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possibles = new;
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}
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for tentative in possibles {
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let mut computer = computer;
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computer.a = tentative;
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let result = computer.run(&code);
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if result == code {
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print_res!("Value: {tentative}");
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return;
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}
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}
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panic!("No solution found");
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}
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pub fn main() -> color_eyre::Result<()> {
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let context = load()?;
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let start = Instant::now();
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let parsed = parsing(&context.input)?;
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let elapsed = humantime::format_duration(start.elapsed());
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let start = Instant::now();
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if context.part == 1 {
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part1(parsed);
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} else {
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part2(parsed);
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}
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let elapsed_part = humantime::format_duration(start.elapsed());
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println!(" Parsing: {elapsed}");
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println!(" Solving: {elapsed_part}");
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Ok(())
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}
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