# Day 6: Chronal Coordinates - Advent of Code 2018

I did the Advent of Code 2018 day 6 challenge in Elixir! Parts one and two are as follows:

``````defmodule Day6 do
def part1(input) do
{_infinites, finites} =
input
|> create_grid()
|> group_by_infinites()

{_coordinates, layout} =
finites
|> Enum.group_by(fn {x, y, _dist} -> {x, y} end)
|> Enum.max_by(fn {_, v} -> length(v) end)

length(layout)
end

def part2(input) do
{max_x, max_y, coordinates} =
input

for x <- 0..max_x,
y <- 0..max_y do
coordinates
|> Enum.reduce(0, fn {point_x, point_y}, acc ->
distance = abs(x - point_x) + abs(y - point_y)
distance + acc
end)
end
|> Enum.filter(&(&1 < 10_000))
|> Enum.count()
end

{max_x, max_y, coordinates} =
input
|> String.trim()
|> String.split("\n", trim: true)
|> Enum.reduce({-1, -1, []}, fn line, {max_x, max_y, coordinates} ->
[x, y] = String.split(line, ", ")
x = String.to_integer(x)
y = String.to_integer(y)
coordinate = {x, y}
max_x = if x > max_x, do: x, else: max_x
max_y = if y > max_y, do: y, else: max_y
{max_x, max_y, [coordinate | coordinates]}
end)

{max_x, max_y, Enum.reverse(coordinates)}
end

defp create_grid({max_x, max_y, coordinates}) do
for x <- 0..max_x,
y <- 0..max_y do
[{px, py, dist1}, {_, _, dist2} | _] =
Enum.map(coordinates, fn {point_x, point_y} ->
distance = abs(x - point_x) + abs(y - point_y)
{point_x, point_y, distance}
end)
|> Enum.sort_by(fn {_, _, distance} -> distance end)

if dist1 == dist2 do
nil
else
cond do
x == 0 ->
{:infinite, px, py}

x == max_x ->
{:infinite, px, py}

y == 0 ->
{:infinite, px, py}

y == max_y ->
{:infinite, px, py}

true ->
{px, py, dist1}
end
end
end
end

defp group_by_infinites(grid) do
Enum.reduce(grid, {MapSet.new(), []}, fn
nil, acc ->
acc

{:infinite, px, py}, {infinites, finites} ->
{MapSet.put(infinites, {px, py}), finites}

{px, py, dist}, {infinites, finites} ->
if MapSet.member?(infinites, {px, py}) do
{infinites, finites}
else
{infinites, [{px, py, dist} | finites]}
end
end)
end
end

# r Day6; :aoc2018 |> :code.priv_dir() |> Path.join("day6.txt") |> Day6.part1()
# r Day6; :aoc2018 |> :code.priv_dir() |> Path.join("day6.txt") |> Day6.part2()
``````

Author

### Simon Escobar Benitez

Colombian Software Engineer (Erlang Solutions)

## Upcoming conferences

Start booking your calendar with more Code Sync conferences happening across the globe. We will be slowly releasing more dates, in the meantime here is what we’ve planned already:

## ARTICLES: 8

### Day 11: Chronal Charge - Advent of Code 2018

I did the Advent of Code 2018 day 11 challenge in Elixir! Parts one and two are as follows:

### Day 10: The Stars Align - Advent of Code 2018

I did the Advent of Code 2018 day 10 challenge in Elixir! Parts one and two are as follows:

### Day 7: The Sum of Its Parts - Advent of Code 2018

I did the Advent of Code 2018 day 7 challenge in Elixir! Parts one and two are as follows:

### Day 5: Alchemical Reduction - Advent of Code 2018

I did the Advent of Code 2018 day 5 challenge in Elixir! Parts one and two are as follows:

### Day 4: Repose Record - Advent of Code 2018

I did the Advent of Code 2018 day 4 challenge in Elixir! Parts one and two are as follows:

### Day 3: No matter how you slice it - Advent of Code 2018

I did the Advent of Code 2018 day 3 challenge in Elixir! Parts one and two are as follows: