44 lines
1.4 KiB
Elixir
44 lines
1.4 KiB
Elixir
defmodule ResistorColorTrio do
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@type color :: :black | :brown | :red | :orange | :yellow | :green | :blue | :violet | :grey | :white
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@type colors :: [color]
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@type unit :: :ohms | :kiloohms | :megaohms | :gigaohms
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defguardp is_giga(value) when value >= 1_000_000_000
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defguardp is_mega(value) when value >= 1_000_000
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defguardp is_kilo(value) when value >= 1_000
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@doc """
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Calculate the resistance value in ohms from resistor colors
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"""
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@spec label(colors) :: {number, unit}
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def label(colors) do
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colors
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|> Enum.take(2)
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|> Enum.map(&code/1)
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|> Kernel.++(zeros(Enum.at(colors, 2)))
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|> Integer.undigits()
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|> with_unit()
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end
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@spec code(color) :: integer()
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defp code(:black), do: 0
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defp code(:brown), do: 1
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defp code(:red), do: 2
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defp code(:orange), do: 3
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defp code(:yellow), do: 4
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defp code(:green), do: 5
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defp code(:blue), do: 6
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defp code(:violet), do: 7
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defp code(:grey), do: 8
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defp code(:white), do: 9
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@spec zeros(color) :: list()
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defp zeros(color), do: List.duplicate(0, code(color))
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@spec with_unit(integer) :: {integer, unit}
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defp with_unit(value) when is_giga(value), do: {div(value, 1_000_000_000), :gigaohms}
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defp with_unit(value) when is_mega(value), do: {div(value, 1_000_000), :megaohms}
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defp with_unit(value) when is_kilo(value), do: {div(value, 1_000), :kiloohms}
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defp with_unit(value), do: {value, :ohms}
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end
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