aoc2020-day5-part1.rs

use std::io::{stdin, Read};

fn main() {
    let mut stdin = stdin();
    let mut buf = [0u8; 7 + 3 + 1];
    let mut max_id = 0;
    while let Ok(()) = stdin.read_exact(&mut buf) {
        let mut row = 0;
        let mut col = 0;
        for (i, c) in buf[..10].iter().enumerate() {
            match c {
                b'B' => row |= 1 << (6 - i),
                b'R' => col |= 1 << (9 - i),
                _ => (),
            }
        }
        max_id = max_id.max((row << 3) + col);
    }
    println!("{}", max_id);
}

aoc2020-day5-part2-optimized.rs

use std::io::{stdin, Read};

fn main() {
    let mut stdin = stdin();
    let mut buf = [0u8; 7 + 3 + 1];
    let mut max_id = 0;
    let mut min_id = 1 << buf.len();
    let mut sum = 0;
    while let Ok(()) = stdin.read_exact(&mut buf) {
        let mut id = 0;
        for (i, c) in buf[..10].iter().enumerate() {
            match c {
                b'R' | b'B' => id |= 1 << (9 - i),
                _ => (),
            }
        }
        max_id = max_id.max(id); min_id = min_id.min(id);
        sum += id;
    }
    fn list_length(a: i32, b: i32) -> i32 {
        (b - a + 1) * (b + a) / 2
    }
    println!("Part 1: {}", max_id);
    println!("Part 2: {}", list_length(min_id, max_id) - sum);
}

aoc2020-day5-part2.rs

use std::io::{stdin, Read};

fn main() {
    let mut stdin = stdin();
    let mut buf = [0u8; 7 + 3 + 1];
    let mut max_id = 0;
    let mut min_id = 1 << buf.len();
    let mut sum = 0;
    while let Ok(()) = stdin.read_exact(&mut buf) {
        let mut row = 0;
        let mut col = 0;
        for (i, c) in buf[..10].iter().enumerate() {
            match c {
                b'B' => row |= 1 << (6 - i),
                b'R' => col |= 1 << (9 - i),
                _ => (),
            }
        }
        let id = (row << 3) + col;
        max_id = max_id.max(id);
        min_id = min_id.min(id);
        sum += id;
    }
    fn list_length(a: i32, b: i32) -> i32 {
        (b - a + 1) * (b + a) / 2
    }
    println!("Part 1: {}", max_id);
    println!("Part 2: {}", list_length(min_id, max_id) - sum);
}

aoc2020-day5.rs

use std::io::{stdin, Read};

fn main() {
    let mut stdin = stdin();
    let mut buf = [0u8; 7 + 3 + 1];
    let mut max_id = 0;
    let mut min_id = 1 << buf.len();
    let mut sum = 0;
    while let Ok(()) = stdin.read_exact(&mut buf) {
        let mut id = 0;
        for (i, c) in buf[..10].iter().enumerate() {
            match c {
                b'R' | b'B' => id |= 1 << (9 - i),
                _ => (),
            }
        }
        max_id = max_id.max(id); min_id = min_id.min(id);
        sum += id;
    }
    fn list_length(a: i32, b: i32) -> i32 {
        (b - a + 1) * (b + a) / 2
    }
    println!("Part 1: {}", max_id);
    println!("Part 2: {}", list_length(min_id, max_id) - sum);
}