# Day 4
```elixir
Mix.install([
{:kino, "~> 0.11.0"}
])
```
## Inputs
```elixir
input_box = Kino.Input.textarea("input")
```
```elixir
input = Kino.Input.read(input_box)
charlist =
input
|> String.split("\n")
|> Enum.map(&String.to_charlist/1)
|> IO.inspect(label: "charlist")
transposed_charlist =
charlist
|> Enum.zip()
|> Enum.map(&Tuple.to_list/1)
|> IO.inspect(label: "transposed charlist")
```
## Part 1
```elixir
horizontal =
charlist
|> Enum.map(&Enum.chunk_every(&1, 4, 1))
|> Enum.map(&Enum.count(&1, fn s -> s === ~c"XMAS" || s === ~c"SAMX" end))
|> Enum.sum()
|> IO.inspect(label: "horizontal")
vertical =
transposed_charlist
|> Enum.map(&Enum.chunk_every(&1, 4, 1))
|> Enum.map(&Enum.count(&1, fn s -> s === ~c"XMAS" || s === ~c"SAMX" end))
|> Enum.sum()
|> IO.inspect(label: "vertical")
defmodule Diagonal do
def check(charlist) do
# Assuming its a square.
check(charlist, length(charlist), length(charlist))
end
defp check(charlist, max_x, max_y) do
for x <- 0..(max_x - 1), y <- 0..(max_y - 1), reduce: 0 do
acc -> acc +
check_br(charlist, x, y, max_x, max_y) +
check_bl(charlist, x, y, max_x, max_y)
end
end
defp check_br(charlist, x, y, max_x, max_y) when
x + 3 < max_x and y + 3 < max_y,
do: check_quad([
Enum.at(charlist, y + 0) |> Enum.at(x + 0),
Enum.at(charlist, y + 1) |> Enum.at(x + 1),
Enum.at(charlist, y + 2) |> Enum.at(x + 2),
Enum.at(charlist, y + 3) |> Enum.at(x + 3)
])
defp check_br(_, _, _, _, _), do: 0
defp check_bl(charlist, x, y, max_x, _max_y) when
y - 3 >= 0 and x + 3 < max_x,
do: check_quad([
Enum.at(charlist, y - 0) |> Enum.at(x + 0),
Enum.at(charlist, y - 1) |> Enum.at(x + 1),
Enum.at(charlist, y - 2) |> Enum.at(x + 2),
Enum.at(charlist, y - 3) |> Enum.at(x + 3)
])
defp check_bl(_, _, _, _, _), do: 0
defp check_quad(~c"XMAS"), do: 1
defp check_quad(~c"SAMX"), do: 1
defp check_quad(_), do: 0
end
diagonal = Diagonal.check(charlist) |> IO.inspect(label: "diagonal")
horizontal + vertical + diagonal
```
## Part 2
```elixir
defmodule MAS do
def check(charlist) do
# Assuming its a square.
# We count everything twice.
check(charlist, length(charlist), length(charlist))
end
defp check(charlist, max_x, max_y) do
for x <- 1..(max_x - 2), y <- 1..(max_y - 2), reduce: 0 do
acc -> acc + (if check_cross(charlist, x, y), do: 1, else: 0)
end
end
defp check_cross(charlist, x, y) do
relevant_chars =
[
Enum.at(charlist, y - 1) |> Enum.at(x - 1),
Enum.at(charlist, y - 1) |> Enum.at(x + 1),
Enum.at(charlist, y - 0) |> Enum.at(x - 0),
Enum.at(charlist, y + 1) |> Enum.at(x - 1),
Enum.at(charlist, y + 1) |> Enum.at(x + 1),
]
IO.inspect(relevant_chars, label: "x=#{x}, y=#{y}")
relevant_chars == ~c"MMASS"
|| relevant_chars == ~c"SSAMM"
|| relevant_chars == ~c"MSAMS"
|| relevant_chars == ~c"SMASM"
end
end
MAS.check(charlist)
```
