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remcopeereboom's solution

to Binary in the Ruby Track

Published at Jul 13 2018 · 6 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.

Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

Note

  • Implement the conversion yourself. Do not use something else to perform the conversion for you.

About Binary (Base-2)

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

  • The rightmost digit gets multiplied by 10^0 = 1
  • The next number gets multiplied by 10^1 = 10
  • ...
  • The nth number gets multiplied by 10^(n-1).
  • All these values are summed.

So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10

Binary is similar, but uses powers of 2 rather than powers of 10.

So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10.


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 binary_test.rb

To include color from the command line:

ruby -r minitest/pride binary_test.rb

Source

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

Submitting Incomplete Solutions

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

binary_test.rb

require 'minitest/autorun'
require_relative 'binary'

# Common test data version: 1.0.0 969717d
class BinaryTest < Minitest::Test
  def test_binary_0_is_decimal_0
    # skip
    assert_equal 0, Binary.to_decimal('0')
  end

  def test_binary_1_is_decimal_1
    skip
    assert_equal 1, Binary.to_decimal('1')
  end

  def test_binary_10_is_decimal_2
    skip
    assert_equal 2, Binary.to_decimal('10')
  end

  def test_binary_11_is_decimal_3
    skip
    assert_equal 3, Binary.to_decimal('11')
  end

  def test_binary_100_is_decimal_4
    skip
    assert_equal 4, Binary.to_decimal('100')
  end

  def test_binary_1001_is_decimal_9
    skip
    assert_equal 9, Binary.to_decimal('1001')
  end

  def test_binary_11010_is_decimal_26
    skip
    assert_equal 26, Binary.to_decimal('11010')
  end

  def test_binary_10001101000_is_decimal_1128
    skip
    assert_equal 1128, Binary.to_decimal('10001101000')
  end

  def test_binary_ignores_leading_zeros
    skip
    assert_equal 31, Binary.to_decimal('000011111')
  end

  def test_2_is_not_a_valid_binary_digit
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('2') }
  end

  def test_a_number_containing_a_non_binary_digit_is_invalid
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('01201') }
  end

  def test_a_number_with_trailing_non_binary_characters_is_invalid
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('10nope') }
  end

  def test_a_number_with_leading_non_binary_characters_is_invalid
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('nope10') }
  end

  def test_a_number_with_internal_non_binary_characters_is_invalid
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('10nope10') }
  end

  def test_a_number_and_a_word_whitespace_spearated_is_invalid
    skip
    assert_raises(ArgumentError) { Binary.to_decimal('001 nope') }
  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 Binary
  def initialize(binary_string)
    @bits = binary_string
  end

  def to_decimal
    bits.reverse.map.with_index { |bit, position| bit * 2**position }.inject(:+)
  end

  def bits
    @bits.chars.map { |x| Integer(x) }
  rescue
    [0]
  end
end

Community comments

Find this solution interesting? Ask the author a question to learn more.
Avatar of remcopeereboom

Should probably have made bits private... I also don't like the rescue statment in the there. I think it's valid to have an empty array of bits if there are none, but it works.

Avatar of kotp

You should at a minimum rescue exactly what you want to react to.

Avatar of kotp

Arrays return nil if the index is not found, representing "nothing" which is appropriate. So this seems like it is idiomatically incorrect for Ruby in relation to how Array is expected to work.

Avatar of remcopeereboom

You should at a minimum rescue exactly what you want to react to.

Yes, that would have been better.

Arrays return nil if the index is not found, representing "nothing" which is appropriate. So this seems like it is idiomatically incorrect for Ruby in relation to how Array is expected to work.

I am not sure what you mean by this. I am not indexing anywhere. I should have specified a default value with inject in case the array is empty. Is that what you are referring to?

Avatar of kotp

Yes, though perhaps it does not matter so much, since it an error would be raised by Integer method early in the call.

Avatar of remcopeereboom

Yes, though perhaps it does not matter so much, since it an error would be raised by Integer method early in the call.

I think that was my original idea, but an empty string will still return nil, not 0.

What can you learn from this solution?

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Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?