128 lines
2.7 KiB
Elixir
128 lines
2.7 KiB
Elixir
defmodule Day12 do
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@example """
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F10
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N3
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F7
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R90
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F11
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"""
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def part1(example \\ false) do
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{x, y, _} =
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example
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|> parse_input()
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|> follow_move_instructions({0, 0, 90})
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manhattan_dist({x, y})
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end
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def part2(example \\ false) do
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example
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|> parse_input()
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|> follow_waypoint_instructions({0, 0}, {10, 1})
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|> manhattan_dist()
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end
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def parse_input(example) do
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if(example, do: @example, else: File.read!("lib/day12/input.txt"))
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|> String.trim()
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|> String.split()
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|> Enum.map(fn <<insn::binary-size(1), rest::binary>> ->
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{insn, String.to_integer(rest)}
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end)
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end
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def follow_move_instructions([], state) do
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state
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end
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def follow_move_instructions([insn | rest], state) do
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follow_move_instructions(rest, move(state, insn))
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end
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def move({x, y, dir}, {"L", val}) do
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new_dir = rem(dir - val, 360)
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new_dir = if new_dir < 0, do: new_dir + 360, else: new_dir
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{x, y, new_dir}
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end
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def move({x, y, dir}, {"R", val}) do
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{x, y, rem(dir + val, 360)}
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end
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def move({_, _, dir} = state, {"F", val}) do
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index = if rem(dir, 180) == 0, do: 1, else: 0
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sign = if dir == 180 || dir == 270, do: -1, else: 1
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put_elem(state, index, elem(state, index) + sign * val)
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end
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def move({x, y, dir}, {"N", val}) do
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{x, y + val, dir}
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end
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def move({x, y, dir}, {"S", val}) do
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{x, y - val, dir}
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end
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def move({x, y, dir}, {"E", val}) do
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{x + val, y, dir}
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end
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def move({x, y, dir}, {"W", val}) do
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{x - val, y, dir}
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end
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def manhattan_dist({x, y}) do
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abs(x) + abs(y)
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end
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def follow_waypoint_instructions([], ship, waypoint) do
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ship
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end
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def follow_waypoint_instructions([insn | rest], ship, waypoint) do
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{new_ship, new_waypoint} = do_waypoint_insn(insn, ship, waypoint)
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follow_waypoint_instructions(rest, new_ship, new_waypoint)
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end
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def do_waypoint_insn({"N", val}, ship, {dx, dy}) do
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{ship, {dx, dy + val}}
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end
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def do_waypoint_insn({"S", val}, ship, {dx, dy}) do
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{ship, {dx, dy - val}}
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end
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def do_waypoint_insn({"E", val}, ship, {dx, dy}) do
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{ship, {dx + val, dy}}
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end
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def do_waypoint_insn({"W", val}, ship, {dx, dy}) do
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{ship, {dx - val, dy}}
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end
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def do_waypoint_insn({"L", val}, ship, {dx, dy}) do
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new_waypoint =
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case val do
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90 ->
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{-dy, dx}
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180 ->
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{-dx, -dy}
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270 ->
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{dy, -dx}
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end
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{ship, new_waypoint}
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end
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def do_waypoint_insn({"R", val}, ship, waypoint) do
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do_waypoint_insn({"L", 360 - val}, ship, waypoint)
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end
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def do_waypoint_insn({"F", val}, {x, y}, {dx, dy} = waypoint) do
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{{x + val * dx, y + val * dy}, waypoint}
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end
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end
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