# 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:

``````defmodule Day10 do
def part1(input) do
{grid, _times} =
input
|> parse_input()
|> iter()

draw(grid)
end

def part2(input) do
{_grid, times} =
input
|> parse_input()
|> iter()

times
end

input
|> String.split("\n", trim: true)
end

defp parse_input(input) do
Enum.map(input, fn line ->
[x, y, vx, vy] =
Regex.scan(~r/(-?\d+)/, line, capture: :all_but_first)
|> List.flatten()
|> Enum.map(&String.to_integer/1)

{{x, y}, {vx, vy}}
end)
end

defp iter(grid) do
distance =
grid
|> layout()
|> distance()

iter(grid, distance, 0)
end

defp iter(grid, previous_distance, times) do
new_grid =
Enum.map(grid, fn {{x, y}, {vx, vy} = v} ->
{{x + vx, y + vy}, v}
end)

distance =
new_grid
|> layout()
|> distance()

if distance <= previous_distance do
iter(new_grid, distance, times + 1)
else
{grid, times}
end
end

defp layout(grid) do
Enum.reduce(grid, {0, 0, 0, 0}, fn {{x, _}, _}, {min_x, max_x, min_y, max_y} ->
{
Enum.min([min_x, x]),
Enum.max([max_x, x]),
Enum.min([min_y, x]),
Enum.max([max_y, x])
}
end)
end

defp distance({min_x, max_x, min_y, max_y}) do
abs(max_x - min_x) + abs(max_y - min_y)
end

defp draw(grid) do
grid =
grid
|> Enum.map(&{elem(&1, 0), 0})
|> Enum.into(%{})

{min_x, max_x, min_y, max_y} = layout(grid)

for y <- min_y..max_y do
for x <- min_x..max_x do
if Map.get(grid, {x, y}) do
IO.write("#")
else
IO.write(".")
end
end

IO.write("\n")
end

grid
end
end

# r Day10; :aoc2018 |> :code.priv_dir() |> Path.join("day10.txt") |> Day10.part1()
# r Day10; :aoc2018 |> :code.priv_dir() |> Path.join("day10.txt") |> Day10.part2()``````

Author

### Simon Escobar Benitez

Colombian Software Engineer (Erlang Solutions)

## 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 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 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:

### 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:

### Day 2: Inventory Management System - Advent of Code 2018

I did the Advent of Code 2018 day 2 challenge in Elixir! Parts one and two are as follows: