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use {
anyhow::{
anyhow,
Context,
Result,
},
std::{
env::args,
fs::File,
io::{
BufRead,
BufReader,
},
path::Path,
},
};
#[derive(Clone,Copy,Debug)]
enum Direction {
North,
South,
East,
West,
}
#[derive(Clone,Copy,Debug)]
struct Point {
x: usize,
y: usize,
}
impl Point {
fn neighbour(&self, dir: Direction) -> Point {
match dir {
Direction::North => Point {x: self.x, y: self.y.overflowing_sub(1).0},
Direction::South => Point {x: self.x, y: self.y + 1},
Direction::East => Point {x: self.x + 1, y: self.y},
Direction::West => Point {x: self.x.overflowing_sub(1).0, y: self.y},
}
}
}
#[derive(Debug)]
struct HeightMap {
size: Point,
levels: Vec<u8>,
}
#[derive(Debug)]
struct VisitMap {
size: Point,
visited: Vec<bool>,
}
impl VisitMap {
fn new(size: Point) -> Self{
let visited = vec![false; size.x*size.y];
Self {
size,
visited,
}
}
fn is_visited(&self, pos: Point) -> bool {
if pos.x >= self.size.x || pos.y >= self.size.y {
return true;
}
self.visited.get(pos.y * self.size.x + pos.x).copied().expect("Invalid index")
}
fn visit(&mut self, pos: Point) {
self.visited[pos.y * self.size.x + pos.x] = true;
}
}
impl HeightMap {
fn level(&self, pos: &Point) -> Result<u8> {
if pos.x >= self.size.x || pos.y >= self.size.y {
return Err(anyhow!("Invalid index {}, {}", pos.x, pos.y));
}
self.levels.get(pos.y * self.size.x + pos.x).copied()
.ok_or_else(|| anyhow!("Invalid index {}, {}", pos.x, pos.y))
}
fn is_lowpoint(&self, pos: &Point) -> bool {
let us = self.level(pos).unwrap_or(0);
let mut ok_count = 0;
let directions = [Direction::North, Direction::South, Direction::East, Direction::West];
directions.into_iter().for_each(|dir| {
let neighbour = pos.neighbour(dir);
match self.level(&neighbour) {
Ok(them) => if us < them { ok_count += 1; },
Err(_) => { ok_count += 1; },
}
});
ok_count == directions.into_iter().count()
}
fn is_highpoint(&self, pos: &Point) -> bool {
self.level(pos).unwrap_or(9) == 9
}
fn basin_size(&self, start: &Point) -> Result<usize> {
let mut unexplored = vec![*start];
let mut pos = None;
let mut size = 0;
let mut seen = VisitMap::new(self.size);
while !unexplored.is_empty() {
if pos.is_none() {
if let Some(new_pos) = unexplored.pop() {
pos = Some(new_pos);
seen.visit(new_pos);
size += 1;
} else {
unreachable!();
}
}
if let Some(cur_pos) = pos {
for dir in [Direction::North, Direction::South, Direction::East, Direction::West] {
if seen.is_visited(cur_pos.neighbour(dir)) {
continue;
}
let neighbour = cur_pos.neighbour(dir);
if self.is_highpoint(&neighbour) {
seen.visit(neighbour);
continue;
} else {
seen.visit(neighbour);
unexplored.push(neighbour);
continue;
}
}
if seen.is_visited(cur_pos.neighbour(Direction::North)) &&
seen.is_visited(cur_pos.neighbour(Direction::South)) &&
seen.is_visited(cur_pos.neighbour(Direction::East)) &&
seen.is_visited(cur_pos.neighbour(Direction::West))
{
pos = None;
}
} else {
unreachable!();
}
}
Ok(size)
}
fn risk_level(&self, pos: &Point) -> Result<usize> {
let level = self.level(pos)?;
Ok(level as usize + 1)
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<HeightMap> {
let reader = BufReader::new(File::open(filename)?);
let mut x_opt = None;
let mut y = 0;
let levels = reader.lines().map(|input| {
let i = input?;
let o: Vec<u8> = i.chars().map(|column| {
let level: u8 = column.to_digit(10).ok_or(anyhow!("Invalid digit"))? as u8;
Ok(level)
}).collect::<Result<Vec<u8>>>()?;
match (x_opt, o.len()) {
(None, len) => x_opt = Some(len),
(Some(this), other) => if this != other {
return Err(anyhow!("Inconsistent map width encountered: {} != {}", this, other));
},
}
y += 1;
Ok(o)
}).collect::<Result<Vec<Vec<u8>>>>()?.into_iter().flatten().collect();
let x = x_opt.ok_or(anyhow!("Could not determine size of heightmap."))?;
let size = Point {
x,
y,
};
Ok(HeightMap {
size,
levels,
})
}
fn part1(map: &HeightMap) -> Result<usize> {
let mut risk_level = 0;
for y in 0..map.size.y {
for x in 0..map.size.x {
if map.is_lowpoint(&Point {x, y}) {
risk_level += map.risk_level(&Point {x, y})?;
}
}
}
Ok(risk_level)
}
fn part2(map: &HeightMap) -> Result<usize> {
let mut basin_sizes = vec![];
for y in 0..map.size.y {
for x in 0..map.size.x {
if map.is_lowpoint(&Point {x, y}) {
basin_sizes.push(map.basin_size(&Point {x, y})?);
}
}
}
basin_sizes.sort_unstable();
Ok(basin_sizes.iter().rev().take(3).product())
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or(anyhow!("Missing input filename"))?;
let input = read_input(filename).context("Could not read input")?;
if do_part_1 {
let solution = part1(&input).context("No solution for part 1")?;
println!("Part1, solution found to be: {}", solution);
}
if do_part_2 {
let solution = part2(&input).context("No solution for part 2")?;
println!("Part2, solution found to be: {}", solution);
}
Ok(())
}
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