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use nom::{
character::complete::{line_ending, one_of},
combinator::{map, map_res},
multi::{many1, separated_list1},
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_9.txt")?;
let height_map = parse_height_map(&input).unwrap().1;
let risk_level_sum: RiskLevel = height_map.risk_levels().into_iter().sum();
dbg!(risk_level_sum);
let mut basin_sizes: Vec<u32> = height_map.basins.iter().map(|basin| basin.size).collect();
basin_sizes.sort_unstable_by(|a, b| b.cmp(a));
dbg!(basin_sizes.iter().take(3).product::<u32>());
Ok(())
}
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
struct Height(u8);
#[derive(
Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, derive_more::Add, derive_more::Sum,
)]
struct RiskLevel(u32);
impl From<Height> for RiskLevel {
fn from(h: Height) -> Self {
RiskLevel(h.0 as u32 + 1)
}
}
#[derive(Debug, Default)]
struct Basin {
size: u32,
}
#[derive(Debug)]
struct HeightMap {
heights: Vec<Vec<Height>>,
low_points: Vec<(usize, usize)>,
basins: Vec<Basin>,
basin_map: Vec<Vec<Option<usize>>>,
}
impl HeightMap {
fn new(heights: Vec<Vec<Height>>) -> HeightMap {
let mut height_map = HeightMap {
heights,
low_points: Vec::new(),
basins: Vec::new(),
basin_map: Vec::new(),
};
height_map.init_low_points();
height_map.init_basins();
height_map
}
}
impl HeightMap {
fn init_low_points(&mut self) {
self.low_points = Vec::new();
for y in 0..self.heights.len() {
for x in 0..self.heights[y].len() {
let current = self.heights[y][x];
let mut is_low_point = true;
let edges = [
(x as isize - 1, y as isize),
(x as isize + 1, y as isize),
(x as isize, y as isize - 1),
(x as isize, y as isize + 1),
];
for edge in edges {
if self
.get_height(edge.0, edge.1)
.map_or(false, |other| other <= current)
{
is_low_point = false;
}
}
if is_low_point {
self.low_points.push((x, y));
}
}
}
}
fn init_basins(&mut self) {
for low_point in self.low_points.clone() {
if self
.get_basin(low_point.0 as isize, low_point.1 as isize)
.is_some()
{
continue;
}
let mut basin = Basin::default();
let basin_index = self.basins.len();
self.set_basin(basin_index, low_point.0, low_point.1);
basin.size += 1;
let mut boundary = vec![low_point];
while boundary.len() > 0 {
let (x, y) = boundary.pop().unwrap();
let edges = [
(x as isize - 1, y as isize),
(x as isize + 1, y as isize),
(x as isize, y as isize - 1),
(x as isize, y as isize + 1),
];
for edge in edges {
if self
.get_height(edge.0, edge.1)
.map_or(false, |other| other != Height(9))
&& self.get_basin(edge.0, edge.1).is_none()
{
let x = edge.0 as usize;
let y = edge.1 as usize;
self.set_basin(basin_index, x, y);
basin.size += 1;
boundary.push((x, y));
}
}
}
self.basins.push(basin);
}
}
fn get_height(&self, x: isize, y: isize) -> Option<Height> {
if x < 0 || y < 0 {
None
} else {
let x = x as usize;
let y = y as usize;
self.heights.get(y).and_then(|row| row.get(x)).cloned()
}
}
fn get_basin(&self, x: isize, y: isize) -> Option<usize> {
if x < 0 || y < 0 {
None
} else {
let x = x as usize;
let y = y as usize;
self.basin_map
.get(y)
.and_then(|row| row.get(x))
.cloned()
.flatten()
}
}
fn set_basin(&mut self, basin: usize, x: usize, y: usize) {
while self.basin_map.len() <= y {
self.basin_map.push(Vec::new());
}
while self.basin_map[y].len() <= x {
self.basin_map[y].push(None);
}
self.basin_map[y][x] = Some(basin);
}
fn risk_levels(&self) -> Vec<RiskLevel> {
self.low_points
.iter()
.copied()
.map(|(x, y)| self.heights[y][x].clone().into())
.collect()
}
}
fn parse_height_map(input: &str) -> IResult<&str, HeightMap> {
map(separated_list1(line_ending, parse_row), HeightMap::new)(input)
}
fn parse_row(input: &str) -> IResult<&str, Vec<Height>> {
many1(parse_height)(input)
}
fn parse_height(input: &str) -> IResult<&str, Height> {
map_res(one_of("0123456789"), |digit| {
digit.to_string().parse().map(Height)
})(input)
}
|
