110 lines
2.3 KiB
Rust
110 lines
2.3 KiB
Rust
mod common;
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use std::{collections::HashSet, iter::repeat};
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type Input = Vec<(char, i32)>;
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type Answer = usize;
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fn processed_input(input: &str) -> Input {
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input
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.lines()
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.map(|l| {
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let mut args = l.split(' ');
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(
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args.next().unwrap().chars().next().unwrap(),
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args.next().unwrap().parse::<i32>().unwrap(),
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)
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})
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.collect()
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}
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fn follow((hx, hy): (i32, i32), (tx, ty): (i32, i32)) -> (i32, i32) {
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let (dx, dy) = (tx.abs_diff(hx), ty.abs_diff(hy));
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let (mx, my) = ((hx - tx) / 2, (hy - ty) / 2);
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if dx > 1 && dy > 1 {
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(tx + mx, ty + my)
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} else if dx > 1 {
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(tx + mx, hy)
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} else if dy > 1 {
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(hx, ty + my)
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} else {
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(tx, ty)
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}
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}
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fn both_parts(input: &Input) -> (Answer, Answer) {
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let mut p1: HashSet<(i32, i32)> = HashSet::new();
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let mut h: (i32, i32) = (0, 0);
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let mut t: (i32, i32) = (0, 0);
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let mut p2: HashSet<(i32, i32)> = HashSet::new();
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let mut r: Vec<(i32, i32)> = repeat((0, 0)).take(10).collect();
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for i in input {
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if let Some((x, y)) = match i.0 {
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'L' => Some((-1, 0)),
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'R' => Some((1, 0)),
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'U' => Some((0, -1)),
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'D' => Some((0, 1)),
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_ => None,
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} {
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for _ in 0..i.1 {
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// move part 1 head/tail
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h = (h.0 + x, h.1 + y);
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t = follow(h, t);
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p1.insert(t);
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// move part 2 rope
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r[0] = (r[0].0 + x, r[0].1 + y);
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for s in 1..r.len() {
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r[s] = follow(r[s - 1], r[s]);
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}
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p2.insert(r[r.len() - 1]);
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}
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}
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}
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(p1.len(), p2.len())
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}
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fn main() {
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let input_text = common::day_input(9);
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let input = processed_input(&input_text);
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common::show_both_answers(&both_parts(&input))
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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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const TEST_INPUT: &str = "R 4
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U 4
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L 3
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D 1
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R 4
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D 1
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L 5
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R 2";
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#[test]
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fn test() {
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let input = processed_input(TEST_INPUT);
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assert_eq!(both_parts(&input), (13, 1));
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}
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const TEST_INPUT2: &str = "R 5
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U 8
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L 8
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D 3
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R 17
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D 10
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L 25
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U 20";
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#[test]
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fn part2_test2() {
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let input2 = processed_input(TEST_INPUT2);
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assert_eq!(both_parts(&input2), (88, 36));
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}
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}
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