64 lines
1.6 KiB
Rust
64 lines
1.6 KiB
Rust
use std::collections::HashSet;
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use aoc_runner_derive::{aoc as aoc_run, aoc_generator};
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type Coord = (i32, i32);
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#[aoc_generator(day9)]
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fn parse_input(input: &str) -> Vec<Coord> {
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let mut out = Vec::new();
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let (mut x, mut y) = (0, 0);
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out.push((x, y));
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for line in input.lines() {
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let (dir, num) = line.split_once(' ').unwrap();
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let num: i32 = num.parse().unwrap();
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for _ in 0..num {
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match dir {
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"U" => y += 1,
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"D" => y -= 1,
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"L" => x -= 1,
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"R" => x += 1,
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_ => unreachable!(),
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}
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out.push((x, y));
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}
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}
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out
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}
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#[aoc_run(day9, part1)]
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fn part1(input: &[Coord]) -> usize {
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let mut tail = (0, 0);
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let mut set = HashSet::new();
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set.insert(tail);
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for mv in input {
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tail = new_tail(mv, &tail);
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set.insert(tail);
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}
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set.len()
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}
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#[aoc_run(day9, part2)]
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fn part2(input: &[Coord]) -> usize {
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let mut knots = Vec::from_iter((0..9).map(|_| (0, 0)));
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let mut set = HashSet::new();
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set.insert((0, 0));
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for mv in input {
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let mut head = *mv;
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for knot in knots.iter_mut() {
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*knot = new_tail(&head, knot);
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head = *knot;
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}
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set.insert(*knots.last().unwrap());
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}
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set.len()
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}
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fn new_tail(head: &Coord, tail: &Coord) -> Coord {
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let dy = head.1 - tail.1;
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let dx = head.0 - tail.0;
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match (dx, dy) {
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(m, n) if m.abs() < 2 && n.abs() < 2 => *tail,
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_ => (tail.0 + dx.signum(), tail.1 + dy.signum()),
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}
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}
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