40 lines
1.2 KiB
Plaintext
40 lines
1.2 KiB
Plaintext
defmodule LZW do
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@encode_map Enum.into(0..255, Map.new, &{[&1],&1})
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@decode_map Enum.into(0..255, Map.new, &{&1,[&1]})
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def encode(str), do: encode(to_char_list(str), @encode_map, 256, [])
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defp encode([h], d, _, out), do: Enum.reverse([d[[h]] | out])
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defp encode([h|t], d, free, out) do
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val = d[[h]]
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find_match(t, [h], val, d, free, out)
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end
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defp find_match([h|t], l, lastval, d, free, out) do
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case Map.fetch(d, [h|l]) do
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{:ok, val} -> find_match(t, [h|l], val, d, free, out)
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:error -> d1 = Map.put(d, [h|l], free)
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encode([h|t], d1, free+1, [lastval | out])
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end
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end
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defp find_match([], _, lastval, _, _, out), do: Enum.reverse([lastval | out])
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def decode([h|t]) do
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val = @decode_map[h]
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decode(t, val, 256, @decode_map, val)
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end
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defp decode([], _, _, _, l), do: Enum.reverse(l) |> to_string
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defp decode([h|t], old, free, d, l) do
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val = if h == free, do: old ++ [List.first(old)], else: d[h]
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add = [List.last(val) | old]
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d1 = Map.put(d, free, add)
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decode(t, val, free+1, d1, val++l)
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end
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end
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str = "TOBEORNOTTOBEORTOBEORNOT"
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IO.inspect enc = LZW.encode(str)
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IO.inspect dec = LZW.decode(enc)
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IO.inspect str == dec
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