2020 day12 performance

[TerjeWiigMathisen]

Description

2020 / day12 8x speedup from a custom single-pass parser
Please ignore the spurious day06 commit, I don't know how to get rid of it!

Type of change

• Performance improvement
• Bug fix
• Other

Checklist

• Pull request title and commit messages are clear and informative.
• Documentation has been updated if necessary.
• Code style matches the existing code. This one is somewhat subjective, but try to "fit in" by
  using the same naming conventions. Code should be portable, avoiding any
  architecture-specific intrinsics.
• Tests pass cargo test
• Code is formatted cargo fmt -- `find . -name "*.rs"`
• Code is linted cargo clippy --all-targets --all-features

Formatting and linting also can be executed by running just
(if installed) on the command line at the project root.

[maneatingape]

Nice, I get a roughly 3x speedup.

We can re-use existing parsing utility methods to get the same effect with less code, while keeping the core idea.

[maneatingape]

parse.rs does exactly this byte by byte parsing, exposed as 2 neat typed iterators (one for unsigned number and one for signed) so that you can write:

use crate::util::parse::*;

let amounts = input.input.signed();

Since we also need the direction command use the nifty methods on Iterator to compose 2 iterators into a single iterator over a 2-tuple, e.g.

    let first = input.bytes().filter(u8::is_ascii_uppercase);
    let second = input.iter_signed();

We can then use this (without an intermediate vec) in your core loop that combines part one and part two, e.g. something like:

    let mut part_one = ORIGIN;
    let mut part_two = ORIGIN;
    let mut direction = RIGHT;
    let mut waypoint = Point::new(10, -1);

    for (command, amount) in first.zip(second) {
        match command {
            b'N' => {
                part_one.y -= amount;
                waypoint.y -= amount;
            }
           ...

[maneatingape]

Can omit the rem_euclid if the class from L reflect the rotation e.g. direction = rotate(direction, 360 - amount);