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day_8.rs
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// --- Day 8: Treetop Tree House ---
// The expedition comes across a peculiar patch of tall trees all planted
// carefully in a grid. The Elves explain that a previous expedition planted
// these trees as a reforestation effort. Now, they're curious if this would be
// a good location for a tree house.
// First, determine whether there is enough tree cover here to keep a tree house
// hidden. To do this, you need to count the number of trees that are visible
// from outside the grid when looking directly along a row or column.
// The Elves have already launched a quadcopter to generate a map with the
// height of each tree (your puzzle input). For example:
// 30373
// 25512
// 65332
// 33549
// 35390
// Each tree is represented as a single digit whose value is its height, where 0
// is the shortest and 9 is the tallest.
// A tree is visible if all of the other trees between it and an edge of the
// grid are shorter than it. Only consider trees in the same row or column; that
// is, only look up, down, left, or right from any given tree.
// All of the trees around the edge of the grid are visible - since they are
// already on the edge, there are no trees to block the view. In this example,
// that only leaves the interior nine trees to consider:
// The top-left 5 is visible from the left and top. (It isn't visible from the
// right or bottom since other trees of height 5 are in the way.)
// The top-middle 5 is visible from the top and right.
// The top-right 1 is not visible from any direction; for it to be visible,
// there would need to only be trees of height 0 between it and an edge.
// The left-middle 5 is visible, but only from the right.
// The center 3 is not visible from any direction; for it to be visible, there
// would need to be only trees of at most height 2 between it and an edge.
// The right-middle 3 is visible from the right.
// In the bottom row, the middle 5 is visible, but the 3 and 4 are not.
// With 16 trees visible on the edge and another 5 visible in the interior, a
// total of 21 trees are visible in this arrangement.
// Consider your map; how many trees are visible from outside the grid?
// --- Part Two ---
// Content with the amount of tree cover available, the Elves just need to know
// the best spot to build their tree house: they would like to be able to see a
// lot of trees.
// To measure the viewing distance from a given tree, look up, down, left, and
// right from that tree; stop if you reach an edge or at the first tree that is
// the same height or taller than the tree under consideration. (If a tree is
// right on the edge, at least one of its viewing distances will be zero.)
// The Elves don't care about distant trees taller than those found by the rules
// above; the proposed tree house has large eaves to keep it dry, so they
// wouldn't be able to see higher than the tree house anyway.
// In the example above, consider the middle 5 in the second row:
// 30373
// 25512
// 65332
// 33549
// 35390
// Looking up, its view is not blocked; it can see 1 tree (of height 3).
// Looking left, its view is blocked immediately; it can see only 1 tree (of
// height 5, right next to it).
// Looking right, its view is not blocked; it can see 2 trees.
// Looking down, its view is blocked eventually; it can see 2 trees (one of
// height 3, then the tree of height 5 that blocks its view).
// A tree's scenic score is found by multiplying together its viewing distance
// in each of the four directions. For this tree, this is 4 (found by
// multiplying 1 * 1 * 2 * 2).
// However, you can do even better: consider the tree of height 5 in the middle
// of the fourth row:
// 30373
// 25512
// 65332
// 33549
// 35390
// Looking up, its view is blocked at 2 trees (by another tree with a height of
// 5).
// Looking left, its view is not blocked; it can see 2 trees.
// Looking down, its view is also not blocked; it can see 1 tree.
// Looking right, its view is blocked at 2 trees (by a massive tree of height
// 9).
// This tree's scenic score is 8 (2 * 2 * 1 * 2); this is the ideal spot for the
// tree house.
// Consider each tree on your map. What is the highest scenic score possible for
// any tree?
use std::collections::HashSet;
#[allow(clippy::needless_range_loop)]
pub fn part_1(input: &str) -> usize {
let grid = input
.lines()
.filter(|l| !l.is_empty())
.map(|l| {
l.chars()
.map(|c| (c as isize - '0' as isize))
.collect::<Vec<_>>()
})
.collect::<Vec<_>>();
let mut visible = HashSet::new();
for i in 0..grid.len() {
let mut v = -1;
for j in 0..grid[i].len() {
if grid[i][j] > v {
visible.insert((i, j));
v = grid[i][j]
}
}
}
for i in 0..grid.len() {
let mut v = -1;
for j in (0..grid[i].len()).rev() {
if grid[i][j] > v {
visible.insert((i, j));
v = grid[i][j]
}
}
}
for j in 0..grid[0].len() {
let mut v = -1;
for i in 0..grid.len() {
if grid[i][j] > v {
visible.insert((i, j));
v = grid[i][j]
}
}
}
for j in 0..grid[0].len() {
let mut v = -1;
for i in (0..grid.len()).rev() {
if grid[i][j] > v {
visible.insert((i, j));
v = grid[i][j]
}
}
}
visible.len()
}
fn count_until_including(iter: impl Iterator<Item = bool>) -> usize {
let mut ct = 0;
for v in iter {
ct += 1;
if !v {
break;
}
}
ct
}
pub fn part_2(input: &str) -> usize {
let grid = input
.lines()
.filter(|l| !l.is_empty())
.map(|l| {
l.chars()
.map(|c| (c as isize - '0' as isize))
.collect::<Vec<_>>()
})
.collect::<Vec<_>>();
let mut max_score = 0;
for i in 0..grid.len() {
for j in 0..grid[i].len() {
let h = grid[i][j];
let s1 = count_until_including((i + 1..grid.len()).map(|ii| grid[ii][j] < h));
let s2 = count_until_including((0..i).rev().map(|ii| grid[ii][j] < h));
let s3 = count_until_including((j + 1..grid[i].len()).map(|jj| grid[i][jj] < h));
let s4 = count_until_including((0..j).rev().map(|jj| grid[i][jj] < h));
max_score = max_score.max(s1 * s2 * s3 * s4);
}
}
max_score
}
#[cfg(test)]
pub mod tests {
use crate::day_8::{part_1, part_2};
const INPUTS: &str = r#"30373
25512
65332
33549
35390"#;
#[test]
pub fn test_day_8_example_part1() {
assert_eq!(part_1(INPUTS), 21);
}
#[test]
pub fn test_day_8_part1() {
assert_eq!(part_1(include_str!("input/day_8.txt")), 1835);
}
#[test]
pub fn test_day_8_example_part2() {
assert_eq!(part_2(INPUTS), 8);
}
#[test]
pub fn test_day_8_part2() {
assert_eq!(part_2(include_str!("input/day_8.txt")), 263670);
}
}