# Advent of Code 2024 - Day 12
```elixir
Mix.install([{:kino, github: "livebook-dev/kino"}])
kino_input = Kino.Input.textarea("Please paste your input file: ")
```
## Part 1
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
input = Kino.Input.read(kino_input)
defmodule Garden do
def regions(garden_map) do
garden_map
|> compute_regions([])
|> Enum.map(&MapSet.new/1)
end
def area(region) do
MapSet.size(region)
end
def perimeter(region) do
region
|> Enum.filter(fn tile ->
Enum.any?(
[
{elem(tile, 0) - 1, elem(tile, 1)}, # up
{elem(tile, 0) + 1, elem(tile, 1)}, # down
{elem(tile, 0), elem(tile, 1) - 1}, # left
{elem(tile, 0), elem(tile, 1) + 1} # right
],
&(&1 not in region)
)
end)
|> Enum.map(fn tile ->
Enum.count(
[
{elem(tile, 0) - 1, elem(tile, 1)}, # up
{elem(tile, 0) + 1, elem(tile, 1)}, # down
{elem(tile, 0), elem(tile, 1) - 1}, # left
{elem(tile, 0), elem(tile, 1) + 1} # right
],
&(&1 not in region)
)
end)
|> Enum.sum()
end
defp compute_regions(garden_map, acc) when map_size(garden_map) == 0 do
acc
end
defp compute_regions(garden_map, acc) do
{coords, plant} = Enum.at(garden_map, 0)
{region, garden} = search_region(garden_map, plant, coords, [])
compute_regions(garden, [region | acc])
end
defp search_region(garden, plant, tile, acc) do
if garden[tile] == plant do
garden = Map.delete(garden, tile)
acc = [tile | acc]
neighbors = [
{elem(tile, 0) - 1, elem(tile, 1)}, # up
{elem(tile, 0) + 1, elem(tile, 1)}, # down
{elem(tile, 0), elem(tile, 1) - 1}, # left
{elem(tile, 0), elem(tile, 1) + 1} # right
]
Enum.reduce(neighbors, {acc, garden}, fn neighbor, {acc, garden} ->
search_region(garden, plant, neighbor, acc)
end)
else
{acc, garden}
end
end
end
input
|> String.split("\n", trim: true)
|> Enum.map(&String.to_charlist/1)
|> Enum.with_index()
|> Enum.reduce(%{}, fn {row, row_index}, acc ->
row
|> Enum.with_index()
|> Enum.reduce(acc, fn {plant, column_index}, inner_acc ->
Map.put(inner_acc, {row_index, column_index}, plant)
end)
end)
|> Garden.regions()
|> Enum.reduce(0, fn region, acc ->
acc + Garden.area(region) * Garden.perimeter(region)
end)
```
## Part 2
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
input = Kino.Input.read(kino_input)
defmodule Garden2 do
def regions(garden_map) do
garden_map
|> compute_regions([])
|> Enum.map(&MapSet.new/1)
end
def area(region) do
MapSet.size(region)
end
def sides(region) do
border_tiles =
region
|> border_tiles()
|> Enum.flat_map(fn tile ->
{y, x} = tile
acc = if {y - 1, x} in region, do: [], else: [{tile, :up}]
acc = if {y + 1, x} in region, do: acc, else: [{tile, :down} | acc]
acc = if {y, x - 1} in region, do: acc, else: [{tile, :left} | acc]
if {y, x + 1} in region, do: acc, else: [{tile, :right} | acc]
end)
|> MapSet.new()
count_sides(border_tiles, 0)
end
defp count_sides(border_tiles, acc) do
if MapSet.size(border_tiles) == 0 do
acc
else
{tile, dir} = Enum.min(border_tiles)
border_tiles = remove_border(border_tiles, {tile, dir})
count_sides(border_tiles, acc + 1)
end
end
defp remove_border(border_tiles, {tile, dir} = entry) when dir in [:up, :down] do
if entry in border_tiles do
border_tiles = MapSet.delete(border_tiles, entry)
{y, x} = tile
remove_border(border_tiles, {{y, x + 1}, dir})
else
border_tiles
end
end
defp remove_border(border_tiles, {tile, dir} = entry) when dir in [:left, :right] do
if entry in border_tiles do
border_tiles = MapSet.delete(border_tiles, entry)
{y, x} = tile
remove_border(border_tiles, {{y + 1, x}, dir})
else
border_tiles
end
end
defp border_tiles(region) do
Enum.filter(region, fn tile ->
tile
|> neighbors()
|> Enum.any?(& &1 not in region)
end)
end
defp neighbors({i, j}) do
[
{i - 1, j}, # up
{i + 1, j}, # down
{i, j - 1}, # left
{i, j + 1} # right
]
end
defp compute_regions(garden_map, acc) when map_size(garden_map) == 0 do
acc
end
defp compute_regions(garden_map, acc) do
{coords, plant} = Enum.at(garden_map, 0)
{region, garden} = search_region(garden_map, plant, coords, [])
compute_regions(garden, [region | acc])
end
defp search_region(garden, plant, tile, acc) do
if garden[tile] == plant do
garden = Map.delete(garden, tile)
acc = [tile | acc]
neighbors = [
{elem(tile, 0) - 1, elem(tile, 1)}, # up
{elem(tile, 0) + 1, elem(tile, 1)}, # down
{elem(tile, 0), elem(tile, 1) - 1}, # left
{elem(tile, 0), elem(tile, 1) + 1} # right
]
Enum.reduce(neighbors, {acc, garden}, fn neighbor, {acc, garden} ->
search_region(garden, plant, neighbor, acc)
end)
else
{acc, garden}
end
end
end
input
|> String.split("\n", trim: true)
|> Enum.map(&String.to_charlist/1)
|> Enum.with_index()
|> Enum.reduce(%{}, fn {row, row_index}, acc ->
row
|> Enum.with_index()
|> Enum.reduce(acc, fn {plant, column_index}, inner_acc ->
Map.put(inner_acc, {row_index, column_index}, plant)
end)
end)
|> Garden2.regions()
|> Enum.reduce(0, fn region, acc ->
acc + Garden2.area(region) * Garden2.sides(region)
end)
```
