advent-of-code-2022/src/day_2.rs

#[derive(Debug)]
enum Error {
    InvalidMove,
    InvalidOutcome,
}

#[derive(Clone, PartialEq)]
enum Move {
    Rock,
    Paper,
    Scissors
}

impl Move {
    fn from_str(input: &str) -> Result<Self, Error> {
        match input {
            "A"|"X" => Ok(Self::Rock),
            "B"|"Y" => Ok(Self::Paper),
            "C"|"Z" => Ok(Self::Scissors),
            _       => Err(Error::InvalidMove)
        }
    }

    fn beats(&self) -> Move {
        match self {
            Move::Rock     => Move::Scissors,
            Move::Paper    => Move::Rock,
            Move::Scissors => Move::Paper,
        }
    }

    fn is_beaten_by(&self) -> Move {
        match self {
            Move::Rock     => Move::Paper,
            Move::Paper    => Move::Scissors,
            Move::Scissors => Move::Rock,
        }
    }

    /// I don't really know why, but these moves have different scores
    fn score(&self) -> u64 {
        match self {
            Move::Rock     => 1,
            Move::Paper    => 2,
            Move::Scissors => 3,
        }
    }
}

enum Outcome {
    Win,
    Draw,
    Lose,
}

impl Outcome {
    pub fn from_str(input: &str) -> Result<Self, Error> {
        match input {
            "X" => Ok(Self::Lose),
            "Y" => Ok(Self::Draw),
            "Z" => Ok(Self::Win),
            _   => Err(Error::InvalidOutcome)
        }
    }
}

fn play(player: Move, opponent: Move) -> Outcome {
    if player.beats() == opponent {
        Outcome::Win
    } else if player == opponent {
        Outcome::Draw
    } else {
        Outcome::Lose
    }
}

/// decrypt a rock-paper-scissors strategy guide, run through it and calculate the outcome
pub fn part_1(input: &str) -> u64 {
    let mut score = 0;
    let throws = input.lines();

    for throw in throws {
        let mut throw: Vec<&str> = throw.split_whitespace().take(2).collect();
        let player   = Move::from_str(throw.pop().unwrap()).unwrap();
        let opponent = Move::from_str(throw.pop().unwrap()).unwrap();

        score += player.score();

        match play(player, opponent) {
            Outcome::Win => {
                score += 6;
            }
            Outcome::Draw => {
                score += 3;
            }
            Outcome::Lose => {}
        }
    }

    score
}

/// decrypt a rock-paper-scissors strategy guide, run through it and calculate the outcome
pub fn part_2(input: &str) -> u64 {
    let mut score = 0;
    let throws = input.lines();

    for throw in throws {
        let mut throw: Vec<&str> = throw.split_whitespace().take(2).collect();
        let player   = throw.pop().unwrap();
        let opponent = Move::from_str(throw.pop().unwrap()).unwrap();

        let player = match Outcome::from_str(player).unwrap() {
            Outcome::Win => opponent.is_beaten_by(),
            Outcome::Draw => opponent.clone(),
            Outcome::Lose => opponent.beats(),
        };

        score += player.score();

        match play(player, opponent) {
            Outcome::Win => {
                score += 6;
            }
            Outcome::Draw => {
                score += 3;
            }
            Outcome::Lose => {}
        }
    }

    score
}