106 lines
2.2 KiB
Rust
106 lines
2.2 KiB
Rust
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use std::collections::HashSet;
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use std::fmt::Write;
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use aoc::err;
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const INPUT: &str = include_str!("../input/day08.txt");
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pub fn run() -> aoc::Result<String> {
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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Ok(res)
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}
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fn part1(input: &str) -> aoc::Result<i64> {
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let instructions = input
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.lines()
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.map(|line| line.parse())
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.collect::<aoc::Result<Vec<Instruction>>>()?;
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let mut interpreter = Interpreter::new(instructions);
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let mut set = HashSet::new();
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loop {
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if !set.insert(interpreter.idx) {
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break;
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}
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interpreter.step();
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}
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Ok(interpreter.accumulator)
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}
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struct Interpreter {
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idx: usize,
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accumulator: i64,
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memory: Vec<Instruction>,
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}
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impl Interpreter {
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fn new(instructions: Vec<Instruction>) -> Self {
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Self {
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idx: 0,
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accumulator: 0,
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memory: instructions,
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}
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}
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fn step(&mut self) {
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match self.memory[self.idx] {
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Instruction::Acc(arg) => {
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self.accumulator += arg;
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self.idx += 1;
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}
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Instruction::Jmp(offset) => self.idx = self.idx.wrapping_add(offset as usize),
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Instruction::Nop => self.idx += 1,
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}
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}
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}
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enum Instruction {
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Acc(i64),
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Jmp(i64),
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Nop,
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}
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impl std::str::FromStr for Instruction {
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type Err = aoc::Error;
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fn from_str(s: &str) -> aoc::Result<Self> {
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let space = s.find(' ').ok_or_else(|| err!("couldn't split on space"))?;
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let inst = &s[..space];
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let arg = s[(space + 1)..]
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.parse()
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.map_err(|e| err!("couldn't parse argument for instruction: {}", e))?;
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Ok(match inst {
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"acc" => Self::Acc(arg),
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"jmp" => Self::Jmp(arg),
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"nop" => Self::Nop,
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_ => return Err(err!("unrecognized instruction `{}`", inst)),
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})
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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const PROVIDED: &str = include_str!("../input/day08_provided.txt");
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#[test]
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fn part1_provided() {
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assert_eq!(part1(PROVIDED).unwrap(), 5);
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 1675);
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}
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}
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