146 lines
3.4 KiB
Rust
146 lines
3.4 KiB
Rust
use crate::prelude::*;
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pub fn solution() -> Solution {
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Solution::new(Day::new(9, 2021), part_1, part_2).with_expected(600, 987840)
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}
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type Coordinate = (isize, isize);
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type HeightMap = HashMap<Coordinate, isize>;
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const ADJACENT_OFFSETS: &[Coordinate] = &[
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(-1, 0), // Left
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(1, 0), // Right
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(0, -1), // Up
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(0, 1), // Down
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];
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fn parse_heightmap(input: &str) -> Result<HeightMap> {
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let mut height_map = HeightMap::new();
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for (y, line) in input.lines().enumerate() {
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for (x, height) in line.char_indices() {
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let height = height
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.to_digit(10)
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.ok_or_else(|| eyre!("Invalid input: {}", line))?
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.try_into()?;
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height_map.insert((x.try_into()?, y.try_into()?), height);
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}
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}
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Ok(height_map)
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}
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fn parse_map_bounds(input: &str) -> Result<Coordinate> {
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Ok((
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input
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.lines()
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.next()
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.map(|line| line.chars().count())
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.ok_or_else(|| eyre!("Invalid input: {}", input))?
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.try_into()?,
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input.lines().count().try_into()?,
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))
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}
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fn discover_basins(
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coordinate: Coordinate,
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discovered_coordinates: &mut Vec<Coordinate>,
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height_map: &HeightMap,
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) -> Vec<Coordinate> {
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let mut coordinates = vec![];
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for (x_offset, y_offset) in ADJACENT_OFFSETS {
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let neighbor = (x_offset + coordinate.0, y_offset + coordinate.1);
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if discovered_coordinates.contains(&neighbor) {
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continue;
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}
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discovered_coordinates.push(neighbor);
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match height_map.get(&neighbor) {
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Some(9) | None => continue,
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Some(_) => {
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coordinates.push(neighbor);
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coordinates.append(&mut discover_basins(
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neighbor,
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discovered_coordinates,
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height_map,
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));
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}
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}
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}
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coordinates
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}
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fn part_1(input: &str) -> Result<String> {
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let height_map = parse_heightmap(input)?;
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let map_bounds = parse_map_bounds(input)?;
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let mut risk_level = 0;
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for y in 0..map_bounds.1 {
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'x_loop: for x in 0..map_bounds.0 {
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let coordinate = (x, y);
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let height = height_map
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.get(&coordinate)
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.ok_or_else(|| eyre!("Coordinate {:?} not found", coordinate))?;
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for (x_offset, y_offset) in ADJACENT_OFFSETS {
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let neighbor = (x_offset + x, y_offset + y);
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if let Some(neighbor_height) = height_map.get(&neighbor) {
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if neighbor_height <= height {
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continue 'x_loop;
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}
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}
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}
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risk_level += 1 + height;
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}
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}
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Ok(risk_level.to_string())
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}
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fn part_2(input: &str) -> Result<String> {
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let height_map = parse_heightmap(input)?;
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let map_bounds = parse_map_bounds(input)?;
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let mut basins = vec![];
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let mut discovered_coordinates = vec![];
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for y in 0..map_bounds.1 {
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'x_loop: for x in 0..map_bounds.0 {
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let coordinate = (x, y);
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if discovered_coordinates.contains(&coordinate) {
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continue 'x_loop;
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}
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let height = height_map
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.get(&coordinate)
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.ok_or_else(|| eyre!("Coordinate {:?} not found", coordinate))?;
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if height == &9 {
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continue 'x_loop;
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}
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let mut basin = vec![coordinate];
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discovered_coordinates.push(coordinate);
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basin.append(&mut discover_basins(
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coordinate,
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&mut discovered_coordinates,
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&height_map,
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));
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basins.push(basin.len());
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discovered_coordinates.append(&mut basin);
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}
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}
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Ok(
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basins
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.into_iter()
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.sorted_by(|a, b| b.cmp(a))
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.take(3)
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.product::<usize>()
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.to_string(),
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)
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}
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