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Versions: 327
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Contents
defmodule RailFenceCipher do
@doc """
Encode a given plaintext to the corresponding rail fence ciphertext
"""
@spec encode(String.t, pos_integer) :: String.t
def encode(str, 1), do: str
def encode(str, rails) do
str
|> String.codepoints
|> fill_fence(rails)
|> Enum.join
end
@doc """
Decode a given rail fence ciphertext to the corresponding plaintext
"""
@spec decode(String.t, pos_integer) :: String.t
def decode(str, 1), do: str
def decode(str, rails) do
0..String.length(str) - 1
|> Enum.to_list
|> fill_fence(rails)
|> extract_original(str)
end
defp extract_original(fence, str) do
0..String.length(str) - 1
|> Enum.map(fn i ->
String.at(str, Enum.find_index(fence, &(&1 == i)))
end)
|> Enum.join
end
defp fill_fence(list_chars, rails) do
rail_zigzag_indexes = Enum.concat(Enum.to_list(0..rails - 1), Enum.to_list(rails - 2..1))
create_empty_fence(rails, length(list_chars))
|> set_chars_to_fence(list_chars, rail_zigzag_indexes)
end
defp create_empty_fence(rows, cols) do
0..rows - 1
|> Enum.map(fn _ ->
List.duplicate(nil, cols)
end)
end
defp set_chars_to_fence(fence, chars, pos_in_zigzag) do
chars
|> Enum.with_index
|> Enum.reduce(fence, fn {char, index}, acc ->
rail_ind = Enum.at(pos_in_zigzag, rem(index, length(pos_in_zigzag)))
List.update_at(acc, rail_ind, &(List.update_at(&1, index, fn _ -> char end)))
end)
|> List.flatten
|> Enum.filter(&(&1 != nil))
end
end
Version data entries
327 entries across 327 versions & 1 rubygems