# Day 8
## Setup
```elixir
Mix.install([:kino])
```
```elixir
input =
Kino.Input.textarea("Paste input here",
default: """
30373
25512
65332
33549
35390
"""
)
```
```elixir
trees = Kino.Input.read(input)
forest =
trees
|> String.splitter("\n", trim: true)
|> Stream.with_index()
|> Stream.flat_map(fn {row, y} ->
row
|> String.splitter("", trim: true)
|> Stream.with_index()
|> Stream.map(fn {height, x} -> {{x, y}, String.to_integer(height)} end)
end)
|> Enum.into(%{})
```
## Part 1
```elixir
defmodule Forest do
def is_visible?(_, _, {0, _}), do: true
def is_visible?(_, _, {_, 0}), do: true
def is_visible?(_, {xm, _}, {xm, _}), do: true
def is_visible?(_, {_, ym}, {_, ym}), do: true
def is_visible?(forest, {forest_width, forest_length}, {x, y}) do
tree_height = forest[{x, y}]
Enum.all?((x - 1)..0, fn n -> forest[{n, y}] < tree_height end) or
Enum.all?((x + 1)..forest_width, fn n -> forest[{n, y}] < tree_height end) or
Enum.all?((y - 1)..0, fn n -> forest[{x, n}] < tree_height end) or
Enum.all?((y + 1)..forest_length, fn n -> forest[{x, n}] < tree_height end)
end
end
{forest_width, forest_length} =
Enum.reduce(forest, {0, 0}, fn {{x, y}, _}, {max_x, max_y} ->
{max(x, max_x), max(y, max_y)}
end)
forest
|> Enum.filter(fn {coords, _} ->
Forest.is_visible?(forest, {forest_width, forest_length}, coords)
end)
|> Enum.count()
```
## Part 2
```elixir
defmodule Part2 do
def scenic_score(_forest, _dims, {0, _}), do: 0
def scenic_score(_forest, _dims, {_, 0}), do: 0
def scenic_score(_, {xm, _}, {xm, _}), do: 0
def scenic_score(_, {_, ym}, {_, ym}), do: 0
def scenic_score(forest, {forest_width, forest_length}, {x, y}) do
tree_height = forest[{x, y}]
up =
(y - 1)..0
|> Enum.reduce_while(0, fn n, acc ->
if forest[{x, n}] < tree_height, do: {:cont, acc + 1}, else: {:halt, acc + 1}
end)
left =
(x - 1)..0
|> Enum.reduce_while(0, fn n, acc ->
if forest[{n, y}] < tree_height, do: {:cont, acc + 1}, else: {:halt, acc + 1}
end)
right =
(x + 1)..forest_width
|> Enum.reduce_while(0, fn n, acc ->
if forest[{n, y}] < tree_height, do: {:cont, acc + 1}, else: {:halt, acc + 1}
end)
down =
(y + 1)..forest_length
|> Enum.reduce_while(0, fn n, acc ->
if forest[{x, n}] < tree_height, do: {:cont, acc + 1}, else: {:halt, acc + 1}
end)
up * down * left * right
end
end
forest
|> Stream.map(fn {coords, _} ->
Part2.scenic_score(forest, {forest_width, forest_length}, coords)
end)
|> Enum.max()
```
