91 lines
2 KiB
Elixir
91 lines
2 KiB
Elixir
defmodule Day9 do
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def init_state(p) when p == :part1 do
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{ [ {0,0}, {0,0} ], MapSet.new() }
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end
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def init_state(p) when p == :part2 do
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{ [ {0,0}, {0,0}, {0,0}, {0,0}, {0,0}, {0,0}, {0,0}, {0,0}, {0,0}, {0,0}], MapSet.new() }
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end
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def execute(line, state) when line == "" do
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state
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end
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def execute(line, state) do
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[command, count] = line |> String.split(" ");
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{ count, _ } = Integer.parse(count);
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Enum.reduce(
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1..count,
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state,
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fn (_, state) ->
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{ rope, tail_positions } = state
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rope = command
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|> get_movement_direction()
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|> move_head(rope)
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{ rope, MapSet.put(tail_positions, List.last(rope)) }
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end
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);
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end
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def get_answer(state) do
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{_, tail_positions } = state
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MapSet.size(tail_positions)
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end
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defp move_head(direction, rope) do
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[head | tail ] = rope
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move_rope([add_2_tuple(head, direction)], tail)
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end
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defp move_rope(good, bad) when bad == [] do
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good
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end
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defp move_rope(good, bad) do
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leader = good |> List.last()
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[ follower | tail ] = bad
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move_rope(good ++ [keep_min_distance(follower, leader, 1)], tail)
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end
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defp keep_min_distance(tail, head, min_distance) do
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difference = distance_vector(tail, head)
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if max_coord_difference(tail, head) <= min_distance do
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tail
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else
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{a, b} = difference
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megan = fn (x) -> if x != 0 do
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if x > 0 do 1 else -1 end
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else
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0
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end
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end
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add_2_tuple(tail, {megan.(a), megan.(b)})
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end
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end
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defp get_movement_direction(direction) do
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case direction do
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"R" -> {1, 0}
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"L" -> {-1, 0}
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"U" -> {0, 1}
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"D" -> {0, -1}
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end
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end
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defp add_2_tuple(x, y) do
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{ elem(x,0) + elem(y,0), elem(x,1) + elem(y,1) }
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end
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defp distance_vector(x, y) do
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{ elem(y,0) - elem(x,0), elem(y,1) - elem(x,1) }
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end
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defp max_coord_difference(x, y) do
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{a, b} = { abs(elem(x,0)-elem(y,0)), abs(elem(x,1)-elem(y,1)) }
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max(a, b)
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end
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end
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