Rail Fence Cipher #rdaily

rchiper.rb

class RCipher

  def take(s, n, stream)
    x = 0
    val = s
    acc = []
    while x < n do
      val = stream.call(val)
      acc.push(val)
      x += 1
    end
    acc
  end

  def rail_stream(num_rails)
    plus = ->(n) { n + 1 }
    minus = ->(n) { n - 1 }
    op = plus
    next_value = ->(n) do
      if n <= 1
        op = plus
      elsif n >= num_rails
        op = minus
      end
      op.call(n)
    end
  end

  def zip_sort(list1, list2)
    indices = {}
    list1.zip(list2).each do |(l, r)|
      indices[l] ||= []
      indices[l].push(r)
    end
    list1.sort.uniq.inject([]) {|a, i| a + indices[i] }
  end

  def enc_list(n, list)
    s = take(0, list.size, rail_stream(n))
    zip_sort(s, list)
  end

  def enc(n, string)
    enc_list(n, string.split("")).join("")
  end

  def dec(n, string)
    o = enc_list(n, (1..string.size).to_a)
    zip_sort(o, string.split("")).join("")
  end
end