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to Hexadecimal in the Ruby Track

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

Convert a hexadecimal number, represented as a string (e.g. "10af8c"), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).

On the web we use hexadecimal to represent colors, e.g. green: 008000, teal: 008080, navy: 000080).

The program should handle invalid hexadecimal strings.


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 hexadecimal_test.rb

To include color from the command line:

ruby -r minitest/pride hexadecimal_test.rb

Source

All of Computer Science http://www.wolframalpha.com/examples/NumberBases.html

Submitting Incomplete Solutions

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

hexadecimal_test.rb

require 'minitest/autorun'
require_relative 'hexadecimal'

class HexadecimalTest < Minitest::Test
  def test_hex_1_is_decimal_1
    assert_equal 1, Hexadecimal.new('1').to_decimal
  end

  def test_hex_c_is_decimal_12
    skip
    assert_equal 12, Hexadecimal.new('c').to_decimal
  end

  def test_hex_10_is_decimal_16
    skip
    assert_equal 16, Hexadecimal.new('10').to_decimal
  end

  def test_hex_af_is_decimal_175
    skip
    assert_equal 175, Hexadecimal.new('af').to_decimal
  end

  def test_hex_100_is_decimal_256
    skip
    assert_equal 256, Hexadecimal.new('100').to_decimal
  end

  def test_hex_19ace_is_decimal_105166
    skip
    assert_equal 105_166, Hexadecimal.new('19ace').to_decimal
  end

  def test_invalid_hex_is_decimal_0
    skip
    assert_equal 0, Hexadecimal.new('carrot').to_decimal
  end

  def test_black
    skip
    assert_equal 0, Hexadecimal.new('000000').to_decimal
  end

  def test_white
    skip
    assert_equal 16_777_215, Hexadecimal.new('ffffff').to_decimal
  end

  def test_yellow
    skip
    assert_equal 16_776_960, Hexadecimal.new('ffff00').to_decimal
  end
end
# frozen_string_literal: true

class Hexadecimal
  HEX_DIGITS = "0123456789ABCDEF"
  private_constant :HEX_DIGITS
  HEX_STRING = /\A[#{HEX_DIGITS}]+\z/
  private_constant :HEX_STRING
  BASE = 16
  private_constant :BASE

  def initialize(string)
    @string = string.upcase
  end

  def to_decimal
    return 0 unless string.match?(HEX_STRING)
    string.chars.reverse.each.with_index.sum(&method(:hex_to_dec))
  end

  private

  attr_reader :string

  def hex_to_dec((hex_character, exponent))
    HEX_DIGITS.index(hex_character) * BASE**exponent
  end
end

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