49 lines
1.3 KiB
Plaintext
49 lines
1.3 KiB
Plaintext
defmodule LZW do
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def encode(str), do: encode(to_char_list(str), init, 256, [])
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defp encode([h], d, _, out), do: Enum.reverse([Dict.get(d, [h]) | out])
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defp encode([h|t], d, free, out) do
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val = Dict.get(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 Dict.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 ->
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d1 = Dict.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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defp init, do: init(255, Map.new)
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defp init(0, d), do: d
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defp init(n, d), do: init(n-1, Dict.put(d,[n],n))
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def decode([h|t]) do
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d = init1(Map.new)
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val = Dict.get(d, h)
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decode(t, val, 256, d, 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 = Dict.get(d, h)
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add = [List.last(val) | old]
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d1 = Dict.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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defp init1(d), do: init1(255, d)
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defp init1(0, d), do: d
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defp init1(n, d), do: init1(n-1, Dict.put(d, n, [n]))
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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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