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lujanfernaud's solution

to Run Length Encoding in the Ruby Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Implement run-length encoding and decoding.

Run-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.


For installation and learning resources, refer to the exercism help page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby run_length_encoding_test.rb

To include color from the command line:

ruby -r minitest/pride run_length_encoding_test.rb

Source

Wikipedia https://en.wikipedia.org/wiki/Run-length_encoding

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

run_length_encoding_test.rb

require 'minitest/autorun'
require_relative 'run_length_encoding'

# Common test data version: 1.0.0 503a57a
class RunLengthEncodingTest < Minitest::Test
  def test_encode_empty_string
    # skip
    input = ''
    output = ''
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_encode_single_characters_only_are_encoded_without_count
    skip
    input = 'XYZ'
    output = 'XYZ'
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_encode_string_with_no_single_characters
    skip
    input = 'AABBBCCCC'
    output = '2A3B4C'
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_encode_single_characters_mixed_with_repeated_characters
    skip
    input = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB'
    output = '12WB12W3B24WB'
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_encode_multiple_whitespace_mixed_in_string
    skip
    input = '  hsqq qww  '
    output = '2 hs2q q2w2 '
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_encode_lowercase_characters
    skip
    input = 'aabbbcccc'
    output = '2a3b4c'
    assert_equal output, RunLengthEncoding.encode(input)
  end

  def test_decode_empty_string
    skip
    input = ''
    output = ''
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_decode_single_characters_only
    skip
    input = 'XYZ'
    output = 'XYZ'
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_decode_string_with_no_single_characters
    skip
    input = '2A3B4C'
    output = 'AABBBCCCC'
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_decode_single_characters_with_repeated_characters
    skip
    input = '12WB12W3B24WB'
    output = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB'
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_decode_multiple_whitespace_mixed_in_string
    skip
    input = '2 hs2q q2w2 '
    output = '  hsqq qww  '
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_decode_lower_case_string
    skip
    input = '2a3b4c'
    output = 'aabbbcccc'
    assert_equal output, RunLengthEncoding.decode(input)
  end

  def test_consistency_encode_followed_by_decode_gives_original_string
    skip
    input = 'zzz ZZ  zZ'
    output = 'zzz ZZ  zZ'
    assert_equal output,
                 RunLengthEncoding.decode(RunLengthEncoding.encode(input))
  end

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  #
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  #
  # In your file, it will look like this:
  #
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  #
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    skip
    assert_equal 3, BookKeeping::VERSION
  end
end
class RunLengthEncoding
  def self.encode(data)
    Encoder.new(data).encode
  end

  def self.decode(data)
    Decoder.new(data).decode
  end
end

class Encoder
  attr_reader :data, :instances

  def initialize(data)
    @data      = data
    @instances = []
  end

  def encode
    separate_instances
    compress_instances
  end

  private

  def separate_instances
    until data.empty?
      character_group = data.match(/((\s|\w)\2*)/)[0]
      instances << data.slice!(character_group)
    end
  end

  def compress_instances
    instances.map do |characters|
      instances = characters.length

      if instances == 1
        characters
      else
        [instances, characters[0]]
      end
    end.join
  end
end

class Decoder
  attr_reader :data, :instances

  def initialize(data)
    @data      = data.split("")
    @instances = []
  end

  def decode
    separate_instances
    expand_instances
  end

  private

  def separate_instances
    until data.empty?
      letter_index = (data.join =~ /\D/) + 1
      instances << data.shift(letter_index)
    end
  end

  def expand_instances
    result = []

    instances.each do |characters|
      characters = characters.join

      if characters.length == 1
        result << characters
        next
      end

      letter_index = characters =~ /\D/
      instances    = characters.match(/\d+/)[0].to_i

      instances.times { result << characters[letter_index] }
    end

    result.join
  end
end

module BookKeeping
  VERSION = 3
end

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