advent-of-code/source/year_2021/day_04/bingo.rs

//! [`Bingo`] code and implementation.

use std::str::FromStr;

use color_eyre::eyre::{eyre, Error};

use super::board::Board;

/// The game of bingo to play with its boards and numbers.
#[derive(Debug)]
pub struct Bingo {
  /// The list of [`Board`]s to play bingo with.
  pub boards: Vec<Board>,
  /// The list of numbers to play.
  pub numbers: Vec<i32>,
}

impl Bingo {
  /// The game loop for part one.
  ///
  /// Loops over the bingo numbers until it finds the first board that has won.
  pub fn play_until_first_win(mut self) -> (Board, i32) {
    for number in self.numbers {
      for board in &mut self.boards {
        board.mark_number(number);

        if board.check() {
          return (board.clone(), number);
        }
      }
    }

    unreachable!()
  }

  /// The game loop for part two.
  ///
  /// Loops over the bingo numbers until only one board is left and then returns
  /// that as the winner.
  pub fn play_until_last_win(mut self) -> (Board, i32) {
    for number in self.numbers {
      for board in &mut self.boards {
        board.mark_number(number);
        board.has_won = board.check();
      }

      if self.boards.len() == 1 {
        return (self.boards.first().unwrap().clone(), number);
      }

      self.boards.retain(|board| !board.has_won);
    }

    unreachable!()
  }
}

impl FromStr for Bingo {
  type Err = Error;

  fn from_str(s: &str) -> Result<Self, Self::Err> {
    let numbers = s
      .split('\n')
      .next()
      .ok_or_else(|| eyre!("Didn't find bingo numbers on the first line"))?
      .split(',')
      .map(str::parse)
      .collect::<Result<_, _>>()?;

    let boards = s
      .split("\n\n")
      .skip(1)
      .map(str::parse)
      .collect::<Result<_, _>>()?;

    Ok(Self { boards, numbers })
  }
}