Sha256: 672cf0e9c68650c00ff31817474ec4a19aaf85b05c40e649223b66394a461e28
Contents?: true
Size: 1.54 KB
Versions: 69
Compression:
Stored size: 1.54 KB
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
69 entries across 69 versions & 1 rubygems