33 lines
1.1 KiB
Text
33 lines
1.1 KiB
Text
defmodule Dutch_national_flag do
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defp ball(:red), do: 1
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defp ball(:white), do: 2
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defp ball(:blue), do: 3
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defp random_ball, do: Enum.random([:red, :white, :blue])
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defp random_ball(n), do: (for _ <- 1..n, do: random_ball())
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defp is_dutch([]), do: true
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defp is_dutch([_]), do: true
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defp is_dutch([b,h|l]), do: ball(b) < ball(h) and is_dutch([h|l])
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defp is_dutch(_), do: false
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def dutch(list), do: dutch([], [], [], list)
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defp dutch(r, w, b, []), do: r ++ w ++ b
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defp dutch(r, w, b, [:red | list]), do: dutch([:red | r], w, b, list)
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defp dutch(r, w, b, [:white | list]), do: dutch(r, [:white | w], b, list)
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defp dutch(r, w, b, [:blue | list]), do: dutch(r, w, [:blue | b], list)
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def problem(n \\ 10) do
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list = random_ball(n)
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if is_dutch(list) do
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IO.puts "The random sequence #{inspect list} is already in the order of the Dutch flag!"
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else
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IO.puts "The starting random sequence is #{inspect list};"
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IO.puts "The ordered sequence is #{inspect dutch(list)}."
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end
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end
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end
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Dutch_national_flag.problem
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