112 lines
2.8 KiB
Rust
112 lines
2.8 KiB
Rust
advent_of_code::solution!(18);
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use aoc_parse::{parser, prelude::*};
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use std::ops::{Add, Div};
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#[derive(Clone, Copy)]
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enum Dir {
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N,
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E,
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S,
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W,
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}
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struct Move {
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dir: Dir,
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count: usize,
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color: String,
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}
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fn parse(input: &str) -> Vec<Move> {
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let p = parser!(lines({ "U" => Dir::N, "R" => Dir::E, "D" => Dir::S, "L" => Dir::W } " " usize " (#" string(digit_hex+) ")"));
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p.parse(input)
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.unwrap()
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.iter()
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.map(|e| Move {
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dir: e.0,
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count: e.1,
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color: e.2.clone(),
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})
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.collect::<Vec<_>>()
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}
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fn get_perimeter(moves: &[Move]) -> Vec<(isize, isize)> {
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let mut c: (isize, isize) = (0, 0);
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let mut r: Vec<(isize, isize)> = vec![];
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r.push(c);
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for m in moves.iter() {
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match m.dir {
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Dir::N => c.0 -= m.count as isize,
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Dir::E => c.1 += m.count as isize,
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Dir::S => c.0 += m.count as isize,
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Dir::W => c.1 -= m.count as isize,
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};
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r.push(c);
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}
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r
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}
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fn distance(s: &(isize, isize), d: &(isize, isize)) -> usize {
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s.0.abs_diff(d.0) + s.1.abs_diff(d.1)
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}
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fn shoelace(coords: &[(isize, isize)]) -> isize {
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let len = coords.len();
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let (area, perimeter) =
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coords
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.iter()
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.enumerate()
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.fold((0isize, 0isize), |(sum, perimeter), (index, c)| {
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let c2 = coords[(index + 1) % len];
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let next_perimeter = perimeter + distance(c, &c2) as isize;
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let next_area = sum + (c.1 * c2.0) - (c.0 * c2.1);
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(next_area, next_perimeter)
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});
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area.abs().add(perimeter).div(2).add(1)
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}
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pub fn part_one(input: &str) -> Option<isize> {
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Some(shoelace(&get_perimeter(&parse(input))))
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}
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pub fn part_two(input: &str) -> Option<isize> {
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let moves = parse(input)
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.iter()
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.map(|m| {
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let mut s = m.color.clone();
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let dir = match s.remove(s.len() - 1) {
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'0' => Dir::E,
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'1' => Dir::S,
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'2' => Dir::W,
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'3' => Dir::N,
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n @ _ => panic!("parsed wrong number {}", n),
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};
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let count = usize::from_str_radix(&s, 16).unwrap();
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Move {
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dir,
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count,
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color: s,
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}
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})
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.collect::<Vec<_>>();
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Some(shoelace(&get_perimeter(&moves)))
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_part_one() {
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let result = part_one(&advent_of_code::template::read_file("examples", DAY));
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assert_eq!(result, Some(62));
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}
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#[test]
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fn test_part_two() {
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let result = part_two(&advent_of_code::template::read_file("examples", DAY));
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assert_eq!(result, Some(952408144115));
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}
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}
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