rle.rb

=begin
  Run length encodingRun-length encoding (RLE) is a simple form of data compression, where runs (consecutive data elements) are replaced by just one data value and count.
  For example we can represent the original 53 characters with only 13.
  "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB" -> "12WB12W3B24WB"
  RLE allows the original data to be perfectly reconstructed from the compressed data, which makes it a lossless data compression."AABCCCDEEEE" -> "2AB3CD4E" -> "AABCCCDEEEE"
  For simplicity, you can assume that the unencoded string will only contain the letters A through Z (either lower or upper case) and whitespace.
  This way data to be encoded will never contain any numbers and numbers inside data to be decoded always represent the count for the following character.
=end

# Usage example
# ruby rle.rb encode WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB
# ruby rle.rb decode 12WB12W3B24WB

class RLE
  def encode(value)
    # (.) grab everything
    # \1+ that repeats more than once
    # and substitute it for the string length and the first character
    puts value.gsub(/(.)\1+/).each { |character| "#{character.length}#{character[0]}" }
  end

  def decode(value)
    # \d grab each number
    # +. and the following character
    # substitute it for the last character returned by the regex multiplied by the integer that comes before it
    puts value.gsub(/\d+./).each { |characters| "#{characters[-1] * characters.chop.to_i}"}
  end
end

throw 'wrong number of arguments' if ARGV.count != 2

RLE.new.send(ARGV.first, ARGV.last)