114 lines
2.5 KiB
Elixir
114 lines
2.5 KiB
Elixir
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defmodule Aoc.Solution.Day09 do
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import Aoc.Utils
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@name "Day 9: Rope Bridge"
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@behaviour Solution
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@impl Solution
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def get_name, do: @name
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@impl Solution
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def present(solution), do: "The rope tail visits #{solution} positions at least once"
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@impl Solution
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def present_again(solution), do: "Solution is #{solution}"
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@impl Solution
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def parse!(raw) do
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raw |> split_lines()
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end
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@impl Solution
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def solve(motions) do
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motions
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|> move()
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|> visited()
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end
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@impl Solution
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def solve_again(_input) do
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"(TBW)"
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end
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def move(motions) when is_list(motions) do
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{_h, _t, seen} = Enum.reduce(motions, {{0, 0}, {0, 0}, MapSet.new()}, &move/2)
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seen
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end
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def move("R " <> steps, acc) do
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change = {0, String.to_integer(steps)}
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{h, t, seen} = acc
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{y, x} = h
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{y, x + String.to_integer(steps)}
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|> follow(change, t, seen)
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end
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def move("L " <> steps, acc) do
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change = {0, 0 - String.to_integer(steps)}
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{h, t, seen} = acc
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{y, x} = h
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{y, x - String.to_integer(steps)}
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|> follow(change, t, seen)
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end
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def move("U " <> steps, acc) do
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change = {String.to_integer(steps), 0}
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{h, t, seen} = acc
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{y, x} = h
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{y + String.to_integer(steps), x}
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|> follow(change, t, seen)
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end
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def move("D " <> steps, acc) do
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change = {0 - String.to_integer(steps), 0}
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{h, t, seen} = acc
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{y, x} = h
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{y - String.to_integer(steps), x}
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|> follow(change, t, seen)
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end
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def follow(h = {y2, x2}, _change, t = {y1, x1}, seen) when y2 == y1 and x2 == x1 do
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{h, t, MapSet.put(seen, t)}
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end
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def follow(h = {_yH, xH}, {change, 0}, {y, _x}, seen) when change > 2 do
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pos = {y + change - 1, xH}
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{h, pos, MapSet.put(seen, pos)}
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end
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def follow(h = {_yH, xH}, {change, 0}, {y, _x}, seen) when change < -2 do
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pos = {y + change + 1, xH}
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{h, pos, MapSet.put(seen, pos)}
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end
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def follow(h = {yH, _xH}, {0, change}, {_y, x}, seen) when change > 2 do
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pos = {yH, x + change - 1}
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{h, pos, MapSet.put(seen, pos)}
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end
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def follow(h = {yH, _xH}, {0, change}, {_y, x}, seen) when change < -2 do
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pos = {yH, x + change + 1}
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{h, pos, MapSet.put(seen, pos)}
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end
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def follow(h = {y2, x2}, _change, t = {y1, x1}, seen) do
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pos =
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case {abs(abs(y2) - abs(y1)), abs(abs(x2) - abs(x1))} do
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{1, 1} -> t
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{1, 0} -> t
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{0, 1} -> t
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end
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{h, pos, MapSet.put(seen, pos)}
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end
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def visited(positions) do
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MapSet.size(positions)
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end
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end
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