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|
use nom::{
character::complete::{anychar, line_ending},
combinator::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_8.txt")?;
let trees = TreeField::parser(&input).unwrap().1;
dbg!(trees.count_visible_trees());
dbg!(trees.find_best_scenic_score());
Ok(())
}
#[derive(Debug)]
struct TreeField {
width: usize,
height: usize,
tree_heights: Vec<Vec<i8>>,
row_height_fields: Vec<HeightField>,
column_height_fields: Vec<HeightField>,
}
#[derive(Default, Debug)]
struct HeightField {
left_breaking_points: Vec<(usize, i8)>,
right_breaking_points: Vec<(usize, i8)>,
}
enum TreeFieldError {
Empty,
NotRectangular,
}
impl TreeField {
fn parser(input: &str) -> IResult<&str, TreeField> {
map_res(
separated_list1(
line_ending,
many1(map_res(anychar, |c: char| c.to_string().parse::<i8>())),
),
TreeField::new,
)(input)
}
fn new(tree_heights: Vec<Vec<i8>>) -> Result<TreeField, TreeFieldError> {
let height = tree_heights.len();
if height == 0 {
return Result::Err(TreeFieldError::Empty);
}
let width = tree_heights[0].len();
let mut row_height_fields = Vec::new();
for row in &tree_heights {
if row.len() != width {
return Result::Err(TreeFieldError::NotRectangular);
}
row_height_fields.push(HeightField::new(&row));
}
let mut column_height_fields = Vec::new();
for column_i in 0..width {
let mut column = Vec::new();
for row in &tree_heights {
column.push(row[column_i].clone());
}
column_height_fields.push(HeightField::new(&column));
}
Ok(TreeField {
width,
height,
tree_heights,
row_height_fields,
column_height_fields,
})
}
fn tree_is_visible(&self, x: usize, y: usize) -> bool {
let tree_height = self.tree_heights[y][x];
let (left_height, right_height) = self.row_height_fields[y].heights_at(x);
let (up_height, down_height) = self.column_height_fields[x].heights_at(y);
tree_height > left_height
|| tree_height > right_height
|| tree_height > up_height
|| tree_height > down_height
}
fn count_visible_trees(&self) -> usize {
let mut count = 0;
for y in 0..self.height {
for x in 0..self.width {
if self.tree_is_visible(x, y) {
count += 1;
}
}
}
count
}
fn tree_scenic_score(&self, x: usize, y: usize) -> usize {
let tree_height = self.tree_heights[y][x];
let (left_height, right_height) = self.row_height_fields[y].heights_at(x);
let left_score = if tree_height > left_height {
x
} else {
let mut count = 0;
let mut shift_x = x;
while shift_x > 0 {
count += 1;
shift_x -= 1;
let height = self.tree_heights[y][shift_x];
if height >= tree_height {
break;
}
}
count
};
let right_score = if tree_height > right_height {
self.width - 1 - x
} else {
let mut count = 0;
let mut shift_x = x;
while shift_x < self.width - 1 {
count += 1;
shift_x += 1;
let height = self.tree_heights[y][shift_x];
if height >= tree_height {
break;
}
}
count
};
let (up_height, down_height) = self.column_height_fields[x].heights_at(y);
let up_score = if tree_height > up_height {
y
} else {
let mut count = 0;
let mut shift_y = y;
while shift_y > 0 {
count += 1;
shift_y -= 1;
let height = self.tree_heights[shift_y][x];
if height >= tree_height {
break;
}
}
count
};
let down_score = if tree_height > down_height {
self.height - 1 - y
} else {
let mut count = 0;
let mut shift_y = y;
while shift_y < self.height - 1 {
count += 1;
shift_y += 1;
let height = self.tree_heights[shift_y][x];
if height >= tree_height {
break;
}
}
count
};
left_score * right_score * up_score * down_score
}
fn find_best_scenic_score(&self) -> usize {
let mut max = 0;
for y in 0..self.height {
for x in 0..self.width {
let next = self.tree_scenic_score(x, y);
max = max.max(next);
}
}
max
}
}
impl HeightField {
fn new(row: &[i8]) -> HeightField {
let mut left_breaking_points = Vec::new();
let mut last_height = -1;
for (i, height) in row.iter().enumerate() {
if height > &last_height {
last_height = height.clone();
left_breaking_points.push((i.clone(), height.clone()));
}
}
let mut right_breaking_points = Vec::new();
last_height = -1;
for (i, height) in row.iter().enumerate().rev() {
if height > &last_height {
last_height = height.clone();
right_breaking_points.push((i.clone(), height.clone()));
}
}
HeightField {
left_breaking_points,
right_breaking_points,
}
}
fn heights_at(&self, i: usize) -> (i8, i8) {
let left = self
.left_breaking_points
.iter()
.filter(|(left_i, _)| left_i < &i)
.map(|(_, height)| height.clone())
.last()
.unwrap_or(-1);
let right = self
.right_breaking_points
.iter()
.filter(|(right_i, _)| right_i > &i)
.map(|(_, height)| height.clone())
.last()
.unwrap_or(-1);
(left, right)
}
}
|
