6.9 KiB
6.9 KiB
AOC2024 Day 12
Section
defmodule Grid2D do
defstruct width: nil, height: nil
@directions %{
straight: [
{1, 0},
{-1, 0},
{0, 1},
{0, -1}
],
diagonal: [
{1, 1},
{1, -1},
{-1, 1},
{-1, -1}
]
}
def new(width, height) do
%Grid2D{width: width, height: height}
end
@doc """
## Examples
iex> Grid2D.index_to_coord(Grid2D.new(5,5), 0)
{0,0}
iex> Grid2D.index_to_coord(Grid2D.new(5,5), 5)
{0,1}
iex> Grid2D.index_to_coord(Grid2D.new(5,5), 6)
{1,1}
iex> Grid2D.index_to_coord(Grid2D.new(5,5), 3)
{3,0}
iex> Grid2D.index_to_coord(Grid2D.new(5,5), 24)
{4, 4}
"""
def index_to_coord(%Grid2D{width: w}, index) do
{rem(index, w), floor(index / w)}
end
@doc """
## Examples
iex> Grid2D.coord_to_index( Grid2D.new(5,5), {0,0})
0
iex> Grid2D.coord_to_index( Grid2D.new(5,5), {4,4})
24
iex> Grid2D.coord_to_index( Grid2D.new(5,5), {2,2})
12
"""
def coord_to_index(%Grid2D{width: w}, {x, y}) do
y * w + x
end
@doc """
## Examples
iex> Grid2D.neighbors({0, 0}, Grid2D.new(5,5)) |> MapSet.new()
MapSet.new([{0, 1}, {1, 1}, {1,0}])
iex> Grid2D.neighbors({2, 2}, Grid2D.new(5,5)) |> MapSet.new()
[{1, 1}, {1, 2}, {1, 3}, {2, 1}, {2, 3}, {3, 1}, {3, 2}, {3, 3}] |> MapSet.new()
iex> Grid2D.neighbors({4, 4}, Grid2D.new(5,5)) |> MapSet.new
[{3, 3}, {3, 4}, {4, 3}] |> MapSet.new
"""
def neighbors(p, g, allowed_directions \\ :all) do
directions(allowed_directions)
|> Stream.map(&add(p, &1))
|> Stream.filter(&is_in_grid?(&1, g))
end
@doc """
Distance from two points in a grid
iex> Grid2D.distance(Grid2D.new(5,5), {0,0}, {0,1}, :radial)
1
iex> Grid2D.distance(Grid2D.new(5,5), {0,0}, {1,1}, :radial)
1
iex> Grid2D.distance(Grid2D.new(5,5), {0,0}, {1,2}, :radial)
2
"""
def distance(grid, p1, p2, type)
def distance(_, {x, y}, {a, b}, :radial), do: max(abs(x - a), abs(y - b))
@doc """
Add two points together pairwise
iex> Grid2D.add({0,0}, {0,1})
{0,1}
iex> Grid2D.add({2,3}, {3,2})
{5,5}
"""
def add({x, y}, {j, k}), do: {x + j, y + k}
@doc """
Test if a point is in a grid
iex> Grid2D.is_in_grid?({1, 2}, %Grid2D{width: 3, height: 4})
true
iex> Grid2D.is_in_grid?({2, 2}, %Grid2D{width: 2, height: 4})
false
"""
def is_in_grid?({x, y}, %Grid2D{width: w, height: h}), do: x < w and y < h and x >= 0 and y >= 0
@spec directions(allowed :: :all | :straight | :diagonal) :: any()
def directions(allowed \\ :all)
def directions(:all), do: directions(:straight) ++ directions(:diagonal)
def directions(:straight), do: @directions |> Map.get(:straight)
def directions(:diagonal), do: @directions |> Map.get(:diagonal)
def mul({x, y}, n), do: {n*x, n*y}
end
defmodule EnumUtil do
def pick_n(enum, n)
def pick_n([], _), do: []
def pick_n([a | rest], n) do
pick_n(rest, n, n, []) ++ pick_n(rest, n, n - 1, [a])
end
defp pick_n([], n, _, acc) do
if acc |> Enum.count == n do
[acc]
else
[]
end
end
defp pick_n(_, _, 0, acc), do: [acc]
defp pick_n([a | rest], n, r, acc) do
pick_n(rest, n, r, acc) ++ pick_n(rest, n, r - 1, [a | acc])
end
end
input = """
"""
lines = input |> String.trim() |> String.split("\n")
height = lines |> Enum.count
width = lines |> Enum.at(0) |> String.length()
tiles = lines |> Stream.with_index() |> Stream.flat_map(fn {line, i} -> line |> String.graphemes() |> Stream.with_index() |> Enum.map(fn {c, j} -> {{j, i}, c} end) end) |> Enum.into(%{})
grid = Grid2D.new(width, height)
defmodule Crawl do
def crawl([], _, _, acc), do: acc
def crawl(points, tiles, grid, acc) do
n = points
|> Enum.flat_map(fn p -> Grid2D.neighbors(p, grid, :straight)
|> Enum.reject(&(MapSet.member?(acc, &1) or Map.get(tiles, &1) != Map.get(tiles, p))) end)
|> Enum.uniq()
# IO.puts("#{inspect(n)}")
crawl(n, tiles, grid, points |> Enum.reduce(acc, fn x, s -> MapSet.put(s, x) end))
end
def crawl(tiles, grid) do
for {pt, _} <- tiles, reduce: {MapSet.new([]),[]} do
{seen, list} ->
if !MapSet.member?(seen, pt) do
visited = Crawl.crawl([pt], tiles, grid, MapSet.new([pt]))
{seen |> MapSet.union(visited), [visited | list]}
else
{seen, list}
end
end |> elem(1)
end
def pricep1(regions) do
for region <- regions, reduce: 0 do
acc ->
area = region |> MapSet.size()
perimeter = 4*area - (region |> MapSet.to_list() |> EnumUtil.pick_n(2) |> Stream.map(
fn [{a,b},{x,y}] ->
if (a == x and abs(b-y) == 1) or (b == y and abs(a-x) == 1) do
2
else
0
end
end
) |> Enum.sum())
acc + area*perimeter
end
end
def rotate90({a, b}), do: {-b, a}
def pricep2(regions, tiles, grid) do
for region <- regions, reduce: 0 do
acc ->
sides = for direction <- Grid2D.directions(:straight) do
for tile <- region,
neighbor = Grid2D.add(tile, direction),
Map.get(tiles, neighbor) != Map.get(tiles, tile),
reduce: {MapSet.new, 0} do
{used, total} ->
if !MapSet.member?(used, tile) do
scan_dir = rotate90(direction)
line = Stream.iterate(1, &(&1 + 1))
|> Stream.map(fn n ->
if rem(n, 2) == 0 do
{:up, div(n,2)}
else
{:down, div(n+1, 2)*-1}
end
end)
|> Stream.map(&({elem(&1, 0), Grid2D.mul(scan_dir, elem(&1, 1))}))
|> Enum.reduce_while(
%{line: MapSet.new, up: true, down: true},
fn {dir, next}, %{line: line} = acc ->
next = Grid2D.add(next, tile)
is_same? = Map.get(tiles, next) == Map.get(tiles, tile)
next_external? = Map.get(tiles, Grid2D.add(next, direction)) != Map.get(tiles, next)
acc = if acc[dir] and Grid2D.is_in_grid?(next, grid) and is_same? and next_external? do
%{acc | line: MapSet.put(line, next)}
else
acc |> Map.put(dir, false)
end
{(if acc[:up] or acc[:down], do: :cont, else: :halt), acc}
end
) |> Map.get(:line)
{used |> MapSet.union(line), total + 1}
else
{used, total}
end
end |> elem(1)
end |> Enum.sum()
area = region |> MapSet.size()
acc + area*sides
end
end
end
regions = Crawl.crawl(tiles, grid)
Crawl.pricep1(regions)
Crawl.pricep2(regions, tiles, grid)