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use std::collections::HashMap;
static DAY: u8 = 8;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", visible_trees(&input));
println!("{DAY}b: {}", highest_scenic_score(&input));
}
#[derive(Default, Debug)]
struct NeighborVisibility {
up: usize,
down: usize,
left: usize,
right: usize,
}
fn visible_trees(input: &[String]) -> usize {
let mut map = Vec::new();
for line in input {
let heights = line.chars().map(|x| x.to_digit(10).unwrap() as usize).collect::<Vec<_>>();
map.push(heights);
}
let mut visibilities = HashMap::<_,NeighborVisibility>::new();
/* visibilities from top to bottom */
for x in 1 .. map[0].len() - 1 {
let mut current_vis = map[0][x];
#[allow(clippy::needless_range_loop)]
for y in 1 .. map.len() - 1 {
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.up = current_vis;
current_vis = current_vis.max(map[y][x]);
}
}
/* visibilities from bottom to top */
for x in 1 .. map[0].len() - 1 {
let mut current_vis = map[map.len()-1][x];
for y in (1 .. map.len() - 1).rev() {
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.down = current_vis;
current_vis = current_vis.max(map[y][x]);
}
}
/* visibilities from left to right */
for y in 1 .. map.len() - 1 {
let mut current_vis = map[y][0];
for x in 1 .. map[0].len() - 1 {
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.left = current_vis;
current_vis = current_vis.max(map[y][x]);
}
}
/* visibilities from right to left */
for y in 1 .. map.len() - 1 {
let mut current_vis = map[y][map[0].len()-1];
for x in (1 .. map[0].len() - 1).rev() {
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.right = current_vis;
current_vis = current_vis.max(map[y][x]);
}
}
let mut total_visible = 2 * (map.len() - 1) + 2 * (map[0].len() - 1);
for (pos, visibility) in visibilities {
let height = map[pos.1][pos.0];
if height > visibility.up || height > visibility.down || height > visibility.left || height > visibility.right {
total_visible += 1;
}
}
total_visible
}
fn highest_scenic_score(input: &[String]) -> usize {
let mut map = Vec::new();
for line in input {
let heights = line.chars().map(|x| x.to_digit(10).unwrap() as usize).collect::<Vec<_>>();
map.push(heights);
}
let mut visibilities = HashMap::<_,NeighborVisibility>::new();
let update_range_vector = |range: &mut [usize; 10], height: usize|{
/* all heights less than the specified one will start with a
new visibility of one; for greater heights the distance
increases by 1. */
for (i, val) in range.iter_mut().enumerate() {
if i <= height as usize {
*val = 1;
} else {
*val += 1;
}
}
};
/* visibilities from top to bottom */
for x in 0 .. map[0].len() {
let mut ranges = [0; 10];
#[allow(clippy::needless_range_loop)]
for y in 0 .. map.len() {
let height = map[y][x];
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.up = ranges[height];
update_range_vector(&mut ranges, height);
}
}
/* visibilities from bottom to top */
for x in 0 .. map[0].len() {
let mut ranges = [0; 10];
for y in (0 .. map.len()).rev() {
let height = map[y][x];
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.down = ranges[height];
update_range_vector(&mut ranges, height);
}
}
/* visibilities from left to right */
for y in 0 .. map.len() {
let mut ranges = [0; 10];
for x in 0 .. map[0].len() {
let height = map[y][x];
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.left = ranges[height];
update_range_vector(&mut ranges, height);
}
}
/* visibilities from right to left */
for y in 0 .. map.len() {
let mut ranges = [0; 10];
for x in (0 .. map[0].len()).rev() {
let height = map[y][x];
let vis_entry = visibilities.entry((x,y)).or_default();
vis_entry.right = ranges[height];
update_range_vector(&mut ranges, height);
}
}
visibilities.values()
.map(|v| v.up * v.down * v.left * v.right)
.max()
.unwrap()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"30373",
"25512",
"65332",
"33549",
"35390",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(visible_trees(&input), 21);
assert_eq!(highest_scenic_score(&input), 8);
}
}
|
