# Advent of Code (2022) Day 8

Dec 8, 2022

### Highlights

• Avert your eyes! This is not code that I am proud of, but it got the job done… I remember seeing some Numberphile or other YouTube video about this problem, but couldn’t find it. I’m sure there is some useful math trick to make this easier. I have lots of wet and inefficient code with hard-coded values.
• The only “trick” I used here was representing the grid as a map with tuples of the positions as keys. It is cool that you can use any data type as a key in Elixir. This is the first time I have ever made use of keys that weren’t strings or atoms.
``````defmodule Day08 do
use AOC

def get_grid() do
input(8)
|> String.split("\n")
|> Enum.with_index
|> Enum.reduce(%{}, fn {row, row_num}, map ->
row
|> String.codepoints
|> Enum.with_index
|> Map.new(fn {height, col_num} -> {{row_num, col_num}, String.to_integer(height)} end)
|> Map.merge(map)
end)
end

def part1 do
grid = get_grid()
grid
|> Enum.map(fn {{row_num, col_num}, height} ->
if (row_num == 0 || row_num == 98 || col_num == 0 || col_num == 98) do
true
else
Enum.any?([
(for col_num <- 0..(col_num-1), do: Map.get(grid, {row_num, col_num}) < height) |> Enum.all?,
(for col_num <- (col_num+1)..98, do: Map.get(grid, {row_num, col_num}) < height) |> Enum.all?,
(for row_num <- 0..(row_num-1), do: Map.get(grid, {row_num, col_num}) < height) |> Enum.all?,
(for row_num <- (row_num+1)..98, do: Map.get(grid, {row_num, col_num}) < height) |> Enum.all?,
])
end
end)
|> Enum.count(&Function.identity/1)
end

def part2 do
grid = get_grid()
grid
|> Enum.map(fn {{row_num, col_num}, height} ->
if (row_num == 0 || row_num == 98 || col_num == 0 || col_num == 98) do
0
else
[
(for col_num <- (col_num-1)..0, do: Map.get(grid, {row_num, col_num})),
(for col_num <- (col_num+1)..98, do: Map.get(grid, {row_num, col_num})),
(for row_num <- (row_num-1)..0, do: Map.get(grid, {row_num, col_num})),
(for row_num <- (row_num+1)..98, do: Map.get(grid, {row_num, col_num})),
]
|> Enum.reduce(1, fn direction, product ->
visible = direction
|> Enum.take_while(fn tree -> tree < height end)
|> (fn blocked -> min(length(blocked) + 1, length(direction)) end).()
(visible) * product
end)
end
end)
|> Enum.max
end

end``````