advent/2021/src/day4.rs

use std::fmt;
use color_eyre::eyre;
use eyre::eyre;


struct Ratchet<T, F>
    where T: Copy,
          F: Fn(T) -> u8,
{
    value: Option<T>,
    getter: F,
}

impl<T, F> Ratchet<T, F>
    where T: Copy,
          F: Fn(T) -> u8
{
    fn new(getter: F) -> Self {
        Ratchet {
            value: None,
            getter,
        }
    }

    fn inc(&mut self, other: T) {
        match self.value {
            Some(v) if (self.getter)(other) <= (self.getter)(v) => (),
            _ => self.value = Some(other),
        };
    }

    fn dec(&mut self, other: T) {
        match self.value {
            Some(v) if (self.getter)(other) >= (self.getter)(v) => (),
            _ => self.value = Some(other),
        };
    }
}


#[derive(Copy, Clone, Default, Debug)]
struct Square {
    value: u8,
    draw_time: Option<u8>,
}


#[derive(Copy, Clone, Default, Debug)]
struct Board {
    squares: [[Square; 5]; 5],
    bingo_time: Option<u8>,
    bingo_value: Option<u8>
}


impl Board {
    fn from(squares: &[Square]) -> eyre::Result<Self> {
        let mut it = squares.iter();
        let mut b = Self::default();
        for row in 0..5 {
            for col in 0..5 {
                match it.next() {
                    Some(sq) => b.squares[row][col] = *sq,
                    None => return Err(eyre!("Not enough values to populate board")),
                }
            }
        }
        Ok(b)
    }

    fn set_bingo(&mut self) {
        let mut board_bingo = Ratchet::new(|sq: Square| sq.draw_time.unwrap()); // these unwraps are safe because we will only call inc() or dec() after ensuring there is a value there
        let mut cols_bingo: [bool; 5] = [true; 5];
        let mut cols_last_drawn: Vec<Ratchet<Square, _>> = (0..5)
            .map(|_i| Ratchet::new(|sq: Square| sq.draw_time.unwrap()))
            .collect();
        // let mut cols_last_drawn: [Ratchet<Square, _>; 5] = [Ratchet::new(|sq: Square| sq.draw_time.unwrap()); 5];
        for row in self.squares {
            let mut row_bingo = true;
            let mut row_last_drawn = Ratchet::new(|sq: Square| sq.draw_time.unwrap());
            for (col, sq) in row.iter().enumerate() {
                match sq.draw_time {
                    Some(_) => {
                        row_last_drawn.inc(*sq);
                        cols_last_drawn[col].inc(*sq);
                    },
                    None => {
                        row_bingo = false;
                        cols_bingo[col] = false;
                        break;
                    }
                }
            }

            if row_bingo {
                let bingo_sq = row_last_drawn.value.unwrap(); // we know there will be a value here if row_bingo is true
                board_bingo.dec(bingo_sq); //
            }
        }

        for col in 0..5 {
            if cols_bingo[col] {
                let bingo_sq = cols_last_drawn[col].value.unwrap(); // similar to above
                board_bingo.dec(bingo_sq);
            }
        }

        if let Some(sq) = board_bingo.value {
            self.bingo_time = sq.draw_time;
            self.bingo_value = Some(sq.value);
        }
    }

    fn score(&self) -> eyre::Result<isize> {
        let bingo_time = match self.bingo_time {
            Some(t) => t,
            None => return Err(eyre!("Cannot find the score of a non-winning board")),
        };
        let mut total = 0;
        for row in self.squares {
            for sq in row {
                if sq.draw_time.is_some() && sq.draw_time.unwrap() > bingo_time {
                    total += sq.value as isize;
                }
            }
        }
        let multiplier = self.bingo_value.unwrap() as isize;
        Ok(total * multiplier)
    }
}

impl fmt::Display for Board {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for row in self.squares {
            write!(f, "|")?;
            for (i, sq) in row.iter().enumerate() {
                let dt = sq.draw_time.map(|dt| format!("{}", dt)).unwrap_or(String::from("__"));
                write!(f, "({}: {})", sq.value, dt)?;
                if i < 4 {
                    write!(f, ", ")?;
                }
            }
            write!(f, "|\n")?;
        }
        if self.bingo_time.is_some() {
            write!(f, "Bingo: ({}: {})", self.bingo_value.unwrap(), self.bingo_time.unwrap())
        }
        else {
            write!(f, "Bingo: (__: __)")
        }
    }
}


fn load(data: &str) -> eyre::Result<Vec<Board>> {
    let mut lines = data.lines().peekable();
    let mut draws: [Option<u8>; 100] = [None; 100]; // indices are the number drawn, values are the position in which it was drawn
    for (i, draw) in lines.next().unwrap().split(',').enumerate() {
        let num = draw.parse::<usize>()?;
        draws[num] = Some(i.try_into().unwrap()); // will panic if there are more than 256 items in this iterator, but there aren't
    }

    let mut boards = Vec::new();
    let mut squares = Vec::new();
    for line in lines {
        for s in line.split_whitespace() {
            let value = s.parse::<u8>()?; // shadows the loop variable I guess?
            let sq = Square {value, draw_time: draws[value as usize]};
            squares.push(sq);
        }
        if squares.len() == 25 {
            boards.push(Board::from(&squares)?);
            boards.last_mut().unwrap().set_bingo();
            squares.clear();
        }
    }

    Ok(boards)
}


fn part1(boards: &[Board]) -> eyre::Result<Board> {
    let winner = boards.iter()
        .filter(|b| b.bingo_time.is_some())
        .min_by_key(|b| b.bingo_time.unwrap());

    match winner {
        Some(w) => Ok(*w),
        None => Err(eyre!("Could not find a winning board")),
    }
}


fn part2(boards: &[Board]) -> eyre::Result<Board> {
    let winner = boards.iter()
        .filter(|b| b.bingo_time.is_some())
        .max_by_key(|b| b.bingo_time.unwrap());

    match winner {
        Some(w) => Ok(*w),
        None => Err(eyre!("Could not find a winning board")),
    }
}


pub fn run(data: &str) -> eyre::Result<(isize, isize)> {
    let boards = load(data)?;
    let winner = part1(&boards)?;
    let loser = part2(&boards)?;
    Ok((winner.score()?, loser.score()?))
}