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# Day 12
## Section
```elixir
example = """
RRRRIICCFF
RRRRIICCCF
VVRRRCCFFF
VVRCCCJFFF
VVVVCJJCFE
VVIVCCJJEE
VVIIICJJEE
MIIIIIJJEE
MIIISIJEEE
MMMISSJEEE
"""
defmodule Day12 do
def map(input) do
for {row, y} <- String.split(input, "\n", trim: true) |> Enum.with_index(),
{p, x} <- String.split(row, "", trim: true) |> Enum.with_index(),
into: %{} do
{{x, y, nil}, p}
end
end
def part1(input) do
map = map(input)
regions(map, map, [Enum.at(map, 0)], [], [], [])
|> Enum.map(fn {list, sides} ->
length(list) * length(sides |> Enum.uniq())
end)
|> Enum.sum()
end
def part2(input) do
map = map(input)
regions(map, map, [Enum.at(map, 0)], [], [], [])
|> Enum.map(fn {list, sides} ->
length(list) * (count_v(sides) + count_h(sides) + length(cross(sides)) * 2)
end)
|> Enum.sum()
end
def cross(sides) do
sides = sides |> Enum.uniq()
for {ax, ay, :v} <- sides,
{bx, by, :v} <- sides,
{cx, cy, :h} <- sides,
{dx, dy, :h} <- sides,
ax == bx,
by - ay == 1,
cy == dy,
dx - cx == 1,
bx == dx,
by == dy do
{cx, ay}
end
end
def count_v(list) do
list
|> Enum.uniq()
|> Enum.filter(&(elem(&1, 2) == :v))
|> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
|> Map.values()
|> Enum.map(fn line ->
line
|> Enum.sort()
|> group([])
|> length()
end)
|> Enum.sum()
end
def count_h(list) do
list
|> Enum.uniq()
|> Enum.filter(&(elem(&1, 2) == :h))
|> Enum.group_by(&elem(&1, 1), &elem(&1, 0))
|> Map.values()
|> Enum.map(fn line ->
line
|> Enum.sort()
|> group([])
|> length()
end)
|> Enum.sum()
end
def group([], groups), do: groups
def group([h | t], []) do
group(t, [[h]])
end
def group([h | t], groups) do
new_groups =
Enum.map(groups, fn g ->
if Enum.find(g, fn i -> abs(h - i) == 1 end) do
[h | g]
else
g
end
end)
if groups == new_groups do
group(t, [[h] | groups])
else
group(t, new_groups)
end
end
def regions(map, dmap, [], plots, sides, acc) do
if p = Enum.at(dmap, 0) do
regions(map, dmap, [p], [], [], [{plots, sides} | acc])
else
[{plots, sides} | acc]
end
end
def regions(map, dmap, [{{x, y, adj}, v} = h | t], plots, sides, acc) do
case {Map.get(dmap, {x, y, nil}), Map.get(map, {x, y, nil})} do
{nil, ^v} ->
regions(map, dmap, t, plots, sides, acc)
{^v, _} ->
directions =
if adj do
{ladx, lady} = adj
reverse = [{ladx * -1, lady * -1}]
[{1, 0}, {-1, 0}, {0, 1}, {0, -1}] -- reverse
else
[{1, 0}, {-1, 0}, {0, 1}, {0, -1}]
end
pns =
for {adx, ady} = adj <- directions do
{{x + adx, y + ady, adj}, v}
end
regions(map, Map.delete(dmap, {x, y, nil}), pns ++ t, [h | plots], sides, acc)
_ ->
sides =
case adj do
{1, 0} ->
[{x, y, :v} | sides]
{-1, 0} ->
[{x + 1, y, :v} | sides]
{0, 1} ->
[{x, y, :h} | sides]
{0, -1} ->
[{x, y + 1, :h} | sides]
nil ->
sides
end
regions(map, dmap, t, plots, sides, acc)
end
end
end
Day12.part1(example)
Day12.part2(example)
```
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