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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 {
Up,
Down,
Left,
Right,
}
#[derive(Clone,Debug,PartialEq)]
struct Position {
x: usize,
y: usize,
}
#[derive(Debug)]
struct Trees {
size: usize,
heights: Vec<u8>,
}
impl Trees {
fn new_with_size(size: usize, heights: Vec<u8>) -> Result<Self> {
let len = heights.len();
if size * size == len {
Ok(Self { size, heights, })
} else {
Err(anyhow!("Could not create Trees: {size}² ≠ {len}."))
}
}
fn size(&self) -> usize {
self.size
}
fn height(&self, position: &Position) -> u8 {
let x = position.x as usize;
let y = position.y as usize;
if let Some(height) = self.heights.get(y * self.size + x) {
*height
} else {
panic!("Invalid attempt to access element x: {x}, y: {y} in Trees with size: {}.",
self.size);
}
}
fn is_visible(&self, position: &Position, direction: Direction) -> bool {
let target_height = self.height(position);
match direction {
Direction::Up => {
for distance in 0..position.y {
let cmp_height = self.height(&Position { x: position.x, y: distance });
if cmp_height >= target_height {
return false;
}
}
},
Direction::Down => {
for distance in (position.y + 1)..self.size {
let cmp_height = self.height(&Position { x: position.x, y: distance });
if cmp_height >= target_height {
return false;
}
}
},
Direction::Left => {
for distance in 0..position.x {
let cmp_height = self.height(&Position { x: distance, y: position.y });
if cmp_height >= target_height {
return false;
}
}
},
Direction::Right => {
for distance in (position.x + 1)..self.size {
let cmp_height = self.height(&Position { x: distance, y: position.y });
if cmp_height >= target_height {
return false;
}
}
},
}
true
}
fn distance(&self, start: &Position, direction: &Direction) -> usize {
let target_height = self.height(start);
let position = start.clone();
let mut distance = 0;
match direction {
Direction::Up => {
for i in (0..position.y).rev() {
let cmp_height = self.height(&Position { x: position.x, y: i });
distance += 1;
if cmp_height >= target_height {
break;
}
}
},
Direction::Down => {
for i in (position.y + 1)..self.size {
let cmp_height = self.height(&Position { x: position.x, y: i });
distance += 1;
if cmp_height >= target_height {
break;
}
}
},
Direction::Left => {
for i in (0..position.x).rev() {
let cmp_height = self.height(&Position { x: i, y: position.y });
distance += 1;
if cmp_height >= target_height {
break;
}
}
},
Direction::Right => {
for i in (position.x + 1)..self.size {
let cmp_height = self.height(&Position { x: i, y: position.y });
distance += 1;
if cmp_height >= target_height {
break;
}
}
},
}
distance
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<Trees> {
let reader = BufReader::new(File::open(filename)?);
let mut size = 0;
let heights = reader.lines().map(
|v| {
size += 1;
let s = v?;
s.bytes().map(|height| match height {
b'0'..=b'9' => Ok(height - b'0'),
_ => Err(anyhow!("Invalid digit: '{height}'")),
}).collect::<Result<Vec<_>>>()
}
).collect::<Result<Vec<_>>>()?.into_iter().flatten().collect();
Trees::new_with_size(size, heights)
}
fn part1(input: &Trees) -> Result<usize> {
let mut positions: Vec<Position> = vec![];
for direction in [Direction::Up, Direction::Down, Direction::Left, Direction::Right].iter() {
for y in 0..input.size() {
for x in 0..input.size() {
let position = Position { x, y };
if input.is_visible(&position, *direction) && !positions.contains(&position) {
positions.push(position);
}
}
}
}
Ok(positions.len())
}
fn part2(input: &Trees) -> Result<usize> {
(0..input.size()).flat_map(|y|
(0..input.size()).map(move |x| {
let position = Position { x, y };
[Direction::Up, Direction::Down, Direction::Left, Direction::Right].iter()
.map(|direction| {
input.distance(&position, direction)
}).product()
}
)).max().ok_or_else(|| anyhow!("Really, a tree patch with a 1-by-1 grid?"))
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or_else(|| 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(())
}
|
