143 lines
3.2 KiB
Rust
143 lines
3.2 KiB
Rust
use std::{
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collections::{HashMap, HashSet},
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fs::read_to_string,
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};
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pub fn day_main() {
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let input = read_to_string("input/day06.txt").unwrap();
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let input = input.trim();
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println!(" part1: {}", part1(input));
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println!(" part2: {}", part2(input));
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}
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type RiddleResult = usize;
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type Point = (i32, i32);
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fn part1(input: &str) -> RiddleResult {
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let (m, pos) = parse(input);
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let dir = '^';
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let visited = get_visited(&m, pos, dir);
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visited.len()
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}
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fn get_visited(
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m: &HashMap<(i32, i32), char>,
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mut pos: (i32, i32),
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mut dir: char,
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) -> HashSet<(i32, i32)> {
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let mut visited = HashSet::new();
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while m.contains_key(&pos) {
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let (x, y) = pos;
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visited.insert(pos);
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let next = match dir {
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'^' => (x, y - 1),
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'v' => (x, y + 1),
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'<' => (x - 1, y),
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'>' => (x + 1, y),
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_ => unreachable!(),
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};
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if let Some('#') = m.get(&next) {
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dir = match dir {
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'^' => '>',
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'v' => '<',
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'<' => '^',
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'>' => 'v',
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_ => unreachable!("asdf"),
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};
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} else {
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pos = next;
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}
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}
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visited
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}
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fn part2(input: &str) -> RiddleResult {
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let (m, pos) = parse(input);
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let dir = '^';
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get_visited(&m, pos, dir)
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.into_iter()
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.filter(|open| is_loop(&m, *open, pos, dir))
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.count()
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}
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fn parse(input: &str) -> (HashMap<Point, char>, Point) {
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let mut m = HashMap::new();
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let mut pos = None;
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input.lines().enumerate().for_each(|(y, line)| {
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line.char_indices().for_each(|(x, c)| {
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let x = x as i32;
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let y = y as i32;
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if c == '^' {
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pos = Some((x, y));
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m.insert((x, y), '.');
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} else {
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m.insert((x, y), c);
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}
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});
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});
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(m, pos.unwrap())
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}
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fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char) -> bool {
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let mut visited = HashSet::new();
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while m.contains_key(&pos) {
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let (x, y) = pos;
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let next = match dir {
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'^' => (x, y - 1),
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'v' => (x, y + 1),
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'<' => (x - 1, y),
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'>' => (x + 1, y),
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_ => unreachable!(),
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};
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let blocked = next == block || Some(&'#') == m.get(&next);
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if blocked {
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// we only check for loops on a collision to speed things up
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if visited.contains(&(pos, dir)) {
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return true;
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}
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visited.insert((pos, dir));
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dir = match dir {
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'^' => '>',
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'v' => '<',
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'<' => '^',
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'>' => 'v',
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_ => unreachable!("asdf"),
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};
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} else {
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pos = next;
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}
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}
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false
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}
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#[cfg(test)]
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mod test {
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use super::{part1, part2};
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const TEST_INPUT: &str = r"....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...
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";
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#[test]
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fn test1() {
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assert_eq!(part1(TEST_INPUT), 41);
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}
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#[test]
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fn test2() {
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assert_eq!(part2(TEST_INPUT), 6);
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}
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}
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