angelikatyborska's solution to Trinary on the Ruby track

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 trinary number, represented as a string (e.g. '102012'), to its decimal equivalent using first principles.

The program should consider strings specifying an invalid trinary as the value 0.

Trinary numbers contain three symbols: 0, 1, and 2.

The last place in a trinary number is the 1's place. The second to last is the 3's place, the third to last is the 9's place, etc.

# "102012"
    1       0       2       0       1       2    # the number
1*3^5 + 0*3^4 + 2*3^3 + 0*3^2 + 1*3^1 + 2*3^0    # the value
  243 +     0 +    54 +     0 +     3 +     2 =  302

If your language provides a method in the standard library to perform the conversion, pretend it doesn't exist and implement it yourself.

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 trinary_test.rb

To include color from the command line:

ruby -r minitest/pride trinary_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.

trinary_test.rb

require 'minitest/autorun'
require_relative 'trinary'

class TrinaryTest < Minitest::Test
  def test_trinary_1_is_decimal_1
    assert_equal 1, Trinary.new('1').to_decimal
  end

  def test_trinary_2_is_decimal_2
    skip
    assert_equal 2, Trinary.new('2').to_decimal
  end

  def test_trinary_10_is_decimal_3
    skip
    assert_equal 3, Trinary.new('10').to_decimal
  end

  def test_trinary_11_is_decimal_4
    skip
    assert_equal 4, Trinary.new('11').to_decimal
  end

  def test_trinary_100_is_decimal_9
    skip
    assert_equal 9, Trinary.new('100').to_decimal
  end

  def test_trinary_112_is_decimal_14
    skip
    assert_equal 14, Trinary.new('112').to_decimal
  end

  def test_trinary_222_is_26
    skip
    assert_equal 26, Trinary.new('222').to_decimal
  end

  def test_trinary_1122000120_is_32091
    skip
    assert_equal 32_091, Trinary.new('1122000120').to_decimal
  end

  def test_invalid_trinary_is_decimal_0
    skip
    assert_equal 0, Trinary.new('carrot').to_decimal
  end

  def test_invalid_trinary_with_digits_is_decimal_0
    skip
    assert_equal 0, Trinary.new('0a1b2c').to_decimal
  end

  def test_invalid_trinary_with_multiline_string
    skip
    assert_equal 0, Trinary.new("Invalid\n201\nString").to_decimal
  end

  def test_number_out_of_range
    skip
    assert_equal 0, Trinary.new('4').to_decimal
  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.
  #  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.htm
  def test_bookkeeping
    skip
    assert_equal 1, BookKeeping::VERSION
  end
end

class Trinary
  SYMBOLS = %w{0 1 2}
  BASE = 3

  def initialize(string)
    @chars = string.chars.reverse
  end

  def to_decimal
    return 0 unless all_chars_valid?

    @chars.each_with_index.inject(0) do |sum, (char, i)|
      sum + ( SYMBOLS.find_index(char) * BASE**i )
    end
  end

  private

  def all_chars_valid?
    @chars.all? { |char| SYMBOLS.include? char }
  end
end

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angelikatyborska's solution

to Trinary in the Ruby Track