Solution for Advent of Code 2017 Day 8

day08.rs

use std::time::Instant;

use rustc_hash::FxHashMap;

const INPUT: &str = include_str!("inputs/day08.txt");

enum Modifier {
    Increment(isize),
    Decrement(isize),
}

impl Modifier {
    fn new(what: &str, quantity: &str) -> Self {
        match what {
            "inc" => Self::Increment(quantity.parse::<isize>().unwrap()),
            _ => Self::Decrement(quantity.parse::<isize>().unwrap()),
        }
    }

    fn apply(&self, to: &mut isize) {
        match self {
            Self::Increment(q) => *to += q,
            Self::Decrement(q) => *to -= q,
        }
    }
}

enum Comparator {
    Equal,
    NotEqual,
    Less,
    LessEqual,
    Greater,
    GreaterEqual,
}

impl Comparator {
    fn eval(&self, lhs: isize, rhs: isize) -> bool {
        match self {
            Comparator::Equal => lhs == rhs,
            Comparator::NotEqual => lhs != rhs,
            Comparator::Less => lhs < rhs,
            Comparator::LessEqual => lhs <= rhs,
            Comparator::Greater => lhs > rhs,
            Comparator::GreaterEqual => lhs >= rhs,
        }
    }
}

impl From<&str> for Comparator {
    fn from(value: &str) -> Self {
        match value {
            "==" => Comparator::Equal,
            "!=" => Comparator::NotEqual,
            "<" => Comparator::Less,
            "<=" => Comparator::LessEqual,
            ">" => Comparator::Greater,
            ">=" => Comparator::GreaterEqual,
            _ => panic!("bug"),
        }
    }
}

struct Condition<'a> {
    register: &'a str,
    comp: Comparator,
    value: isize,
}

impl<'a> Condition<'a> {
    fn eval(&self, registers: &FxHashMap<&str, isize>) -> bool {
        self.comp
            .eval(*registers.get(self.register).unwrap_or(&0), self.value)
    }

    fn new(register: &'a str, comp: &str, value: &str) -> Self {
        Self {
            register,
            comp: comp.into(),
            value: value.parse::<isize>().unwrap(),
        }
    }
}

struct Instruction<'a> {
    register: &'a str,
    modifier: Modifier,
    condition: Condition<'a>,
}

impl<'a> Instruction<'a> {
    fn parse(input: &'a str) -> Self {
        let mut parts = input.split_whitespace().filter(|&v| v != "if");
        Instruction {
            register: parts.next().unwrap(),
            modifier: Modifier::new(parts.next().unwrap(), parts.next().unwrap()),
            condition: Condition::new(
                parts.next().unwrap(),
                parts.next().unwrap(),
                parts.next().unwrap(),
            ),
        }
    }
}

fn parse<'a>(input: &'a str) -> Vec<Instruction<'a>> {
    input.lines().map(Instruction::parse).collect()
}

fn p1(input: &str) -> isize {
    let instructions = parse(input);
    let mut registers = FxHashMap::default();

    for instruction in instructions {
        if instruction.condition.eval(&registers) {
            instruction
                .modifier
                .apply(registers.entry(instruction.register).or_default());
        }
    }

    *registers.values().max().unwrap()
}

fn p2(input: &str) -> isize {
    let instructions = parse(input);
    let mut registers = FxHashMap::default();

    let mut max = isize::MIN;
    for instruction in instructions {
        if instruction.condition.eval(&registers) {
            let reg = registers.entry(instruction.register).or_default();
            instruction.modifier.apply(reg);
            max = max.max(*reg);
        }
    }

    max
}

fn main() {
    let now = Instant::now();
    let solution = p1(INPUT);
    println!("p1 {:?} {}", now.elapsed(), solution);

    let now = Instant::now();
    let solution = p2(INPUT);
    println!("p2 {:?} {}", now.elapsed(), solution);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_p1() {
        let input = "b inc 5 if a > 1\na inc 1 if b < 5\nc dec -10 if a >= 1\nc inc -20 if c == 10";
        assert_eq!(p1(input), 1);
    }

    #[test]
    fn test_p2() {
        let input = "b inc 5 if a > 1\na inc 1 if b < 5\nc dec -10 if a >= 1\nc inc -20 if c == 10";
        assert_eq!(p2(input), 10);
    }
}