day_05.rs

use aoc_runner_derive::aoc;
use std::convert::TryInto;

const TOTAL_SIZE: usize = 10;
const LINE_SIZE: usize = TOTAL_SIZE + 1;

struct Input<'a>(&'a [u8]);

impl<'a> Iterator for Input<'a> {
    type Item = BinarySpacePartitioning;
    fn next(&mut self) -> Option<BinarySpacePartitioning> {
        if self.0.len() >= LINE_SIZE {
            let res = Some(BinarySpacePartitioning(
                self.0[..TOTAL_SIZE].try_into().unwrap(),
            ));
            self.0 = &self.0[LINE_SIZE..];
            res
        } else if self.0.len() >= TOTAL_SIZE {
            let res = Some(BinarySpacePartitioning(
                self.0[..TOTAL_SIZE].try_into().unwrap(),
            ));
            self.0 = &[];
            res
        } else {
            None
        }
    }
}

struct BinarySpacePartitioning([u8; TOTAL_SIZE]);

impl BinarySpacePartitioning {
    fn seat_id(&self) -> usize {
        self.0
            .iter()
            .zip((0..TOTAL_SIZE).rev().map(|i| 1 << i))
            .filter_map(|(&val, i)| Some(i).filter(|_| is_r_or_b(val)))
            .fold(0, |acc, x| acc | x)
    }
}

const MASK: u8 = 0b0000100;

fn is_r_or_b(u: u8) -> bool {
    (u & MASK) == 0
}

#[aoc(day5, part1)]
fn part_01(input: &[u8]) -> usize {
    Input(input).map(|bsp| bsp.seat_id()).max().unwrap()
}

#[aoc(day5, part2)]
fn part_02(input: &[u8]) -> usize {
    let (max, min, sum) = Input(input)
        .map(|bsp| bsp.seat_id())
        .fold((0, usize::MAX, 0), |(acc_max, acc_min, acc_sum), id| {
            (acc_max.max(id), acc_min.min(id), acc_sum + id)
        });
    (min..=max).sum::<usize>() - sum
}

#[test]
fn test_mask() {
    assert_eq!(increase_mask(b'B'), true);
    assert_eq!(increase_mask(b'R'), true);
    assert_eq!(increase_mask(b'F'), false);
    assert_eq!(increase_mask(b'L'), false);
}

#[test]
fn test_seat_ids() {
    assert_eq!(BinarySpacePartitioning(*b"BFFFBBFRRR").seat_id(), 567);
    assert_eq!(BinarySpacePartitioning(*b"FFFBBBFRRR").seat_id(), 119);
    assert_eq!(BinarySpacePartitioning(*b"BBFFBBFRLL").seat_id(), 820);
}