this repo has no description
chore: cleanup 09.2022
+36
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2022/day09.livemd
+36
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2022/day09.livemd
···
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{dir, String.to_integer(steps)}
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end)
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|> Enum.flat_map(fn {dir, steps} -> List.duplicate(dir, steps) end)
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```
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<!-- livebook:{"output":true} -->
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```
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[
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{"L", 1},
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{"R", 1},
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{"L", 1},
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{"U", 1},
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{"R", 2},
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{"U", 1},
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{"D", 2},
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{"R", 2},
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{"U", 1},
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{"D", 2},
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{"U", 2},
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{"L", 2},
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{"D", 1},
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{"U", 1},
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{"D", 2},
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{"L", 2},
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{"D", 1},
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{"L", 2},
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{"D", 2},
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{"L", 1},
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{"U", 2},
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{"R", 2},
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{"L", 1},
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{"D", 2},
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{"L", 2},
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{"R", 2},
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{"D", 2},
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{"L", 1},
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{"U", 1},
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{"R", 1},
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{"U", 1},
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{"L", 1},
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{"D", 1},
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{"R", 1},
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{"U", 2},
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{"D", 2},
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{"R", 1},
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{"U", 1},
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{"R", 1},
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{"L", 1},
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{"U", 1},
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{"R", 1},
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{"D", 1},
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{"L", 1},
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{"U", 1},
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{"R", 1},
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{"D", 1},
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{"U", 1},
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{"D", ...},
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{...},
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...
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]
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["L", "R", "L", "U", "R", "R", "U", "D", "D", "R", "R", "U", "D", "D", "U", "U", "L", "L", "D", "U",
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"D", "D", "L", "L", "D", "L", "L", "D", "D", "L", "U", "U", "R", "R", "L", "D", "D", "L", "L", "R",
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"R", "D", "D", "L", "U", "R", "U", "L", "D", "R", ...]
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```
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```elixir
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defmodule Rope do
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@enforce_keys [:segments]
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defstruct [:segments]
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@start %{x: 0, y: 0}
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defstruct segments: [%{x: 0, y: 0}, %{x: 0, y: 0}]
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-
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def new(length),
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do: %__MODULE__{segments: List.duplicate(@start, length + 1)}
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def run(rope, moves) do
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{_rope, tail_positions} =
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Enum.reduce(moves, {rope, MapSet.new([Rope.last(rope)])}, fn dir, {rope, acc} ->
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new_rope = Rope.move(rope, dir)
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{new_rope, MapSet.put(acc, Rope.last(new_rope))}
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end)
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MapSet.size(tail_positions)
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end
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def last(%__MODULE__{segments: list}), do: List.last(list)
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def move(%__MODULE__{segments: [%{x: x, y: y} | tails]}, dir) do
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head =
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case dir do
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"U" -> %{x: x + 1, y: y}
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"D" -> %{x: x - 1, y: y}
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"L" -> %{x: x, y: y + 1}
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"R" -> %{x: x, y: y - 1}
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"L" -> %{x: x + 1, y: y}
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"R" -> %{x: x - 1, y: y}
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"U" -> %{x: x, y: y + 1}
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"D" -> %{x: x, y: y - 1}
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end
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segments = move_tails([head | tails])
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%__MODULE__{segments: segments}
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%__MODULE__{segments: move_tails([head | tails])}
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end
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defp move_tails([]), do: []
···
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when abs(head.x - tail.x) < 2 and abs(head.y - tail.y) < 2,
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do: rope
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defp move_tails([head, tail | rest])
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when abs(head.y - tail.y) < 2,
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do: [head | move_tails([%{x: head.x - sgn(head.x - tail.x), y: head.y} | rest])]
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defp move_tails([head, tail | rest])
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when abs(head.x - tail.x) < 2,
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do: [head | move_tails([%{x: head.x, y: head.y - sgn(head.y - tail.y)} | rest])]
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defp move_tails([head, tail | rest]),
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do: [
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head
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| move_tails([%{x: head.x - sgn(head.x - tail.x), y: head.y - sgn(head.y - tail.y)} | rest])
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]
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defp move_tails([head, tail | rest]) do
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{dx, dy} = step(head, tail)
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[head | move_tails([%{x: head.x - dx, y: head.y - dy} | rest])]
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end
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def sgn(0), do: 0
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def sgn(n) when n < 0, do: -1
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def sgn(_), do: 1
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defp step(%{x: x1, y: y1}, %{x: x2, y: y2}) do
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{sgn(div(x1 - x2, 2)), sgn(div(y1 - y2, 2))}
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end
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end
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```
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<!-- livebook:{"output":true} -->
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```
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{:module, Rope, <<70, 79, 82, 49, 0, 0, 21, ...>>, {:sgn, 1}}
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{:module, Rope, <<70, 79, 82, 49, 0, 0, 23, ...>>, {:step, 2}}
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```
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```elixir
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rope = Rope.new(1)
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{_rope, tail_positions} =
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moves
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|> Enum.flat_map(fn {dir, steps} -> List.duplicate(dir, steps) end)
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|> Enum.reduce({rope, MapSet.new([Rope.last(rope)])}, fn dir, {rope, acc} ->
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new_rope = Rope.move(rope, dir)
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{new_rope, MapSet.put(acc, Rope.last(new_rope))}
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end)
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## Task 1
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MapSet.size(tail_positions)
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```elixir
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Rope.run(Rope.new(1), moves)
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```
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<!-- livebook:{"output":true} -->
···
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## Task 2
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```elixir
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rope = Rope.new(9)
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{_rope, tail_positions} =
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moves
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|> Enum.flat_map(fn {dir, steps} -> List.duplicate(dir, steps) end)
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|> Enum.reduce({rope, MapSet.new([Rope.last(rope)])}, fn dir, {rope, acc} ->
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new_rope = Rope.move(rope, dir)
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{new_rope, MapSet.put(acc, Rope.last(new_rope))}
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end)
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MapSet.size(tail_positions)
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Rope.run(Rope.new(9), moves)
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```
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<!-- livebook:{"output":true} -->