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w1zeman1p's solution

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
class Hexadecimal
  HEX_TO_DEC = {
    '0' => 0,
    '1' => 1,
    '2' => 2,
    '3' => 3,
    '4' => 4,
    '5' => 5,
    '6' => 6,
    '7' => 7,
    '8' => 8,
    '9' => 9,
    'a' => 10,
    'b' => 11,
    'c' => 12,
    'd' => 13,
    'e' => 14,
    'f' => 15,
  }

  def initialize(input)
    input = '' if input =~ /[^a-f0-9]/
    @input = input.downcase
  end

  def to_decimal
    @input
      .chars
      .reverse
      .map { |c| HEX_TO_DEC[c] }
      .each_with_index
      .inject(0) do |sum, (bit, i)|
        sum + (bit * (16 ** i))
      end
  end
end

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