🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉
Avatar of pruthvi12

pruthvi12's solution

to Dominoes in the Ruby Track

Published at Feb 17 2021 · 0 comments
Instructions
Test suite
Solution

Make a chain of dominoes.

Compute a way to order a given set of dominoes in such a way that they form a correct domino chain (the dots on one half of a stone match the dots on the neighbouring half of an adjacent stone) and that dots on the halves of the stones which don't have a neighbour (the first and last stone) match each other.

For example given the stones [2|1], [2|3] and [1|3] you should compute something like [1|2] [2|3] [3|1] or [3|2] [2|1] [1|3] or [1|3] [3|2] [2|1] etc, where the first and last numbers are the same.

For stones [1|2], [4|1] and [2|3] the resulting chain is not valid: [4|1] [1|2] [2|3]'s first and last numbers are not the same. 4 != 3

Some test cases may use duplicate stones in a chain solution, assume that multiple Domino sets are being used.


For installation and learning resources, refer to the Ruby resources 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 dominoes_test.rb

To include color from the command line:

ruby -r minitest/pride dominoes_test.rb

Submitting Incomplete Solutions

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

dominoes_test.rb

require 'minitest/autorun'
require_relative 'dominoes'

# Common test data version: 2.1.0 b5bc74d
class DominoesTest < Minitest::Test
  def test_empty_input_empty_output
    # skip
    dominoes = []
    assert Dominoes.chain?(dominoes)
  end

  def test_singleton_input_singleton_output
    skip
    dominoes = [[1, 1]]
    assert Dominoes.chain?(dominoes)
  end

  def test_singleton_that_can_not_be_chained
    skip
    dominoes = [[1, 2]]
    refute Dominoes.chain?(dominoes)
  end

  def test_three_elements
    skip
    dominoes = [[1, 2], [3, 1], [2, 3]]
    assert Dominoes.chain?(dominoes)
  end

  def test_can_reverse_dominoes
    skip
    dominoes = [[1, 2], [1, 3], [2, 3]]
    assert Dominoes.chain?(dominoes)
  end

  def test_can_not_be_chained
    skip
    dominoes = [[1, 2], [4, 1], [2, 3]]
    refute Dominoes.chain?(dominoes)
  end

  def test_disconnected_simple
    skip
    dominoes = [[1, 1], [2, 2]]
    refute Dominoes.chain?(dominoes)
  end

  def test_disconnected_double_loop
    skip
    dominoes = [[1, 2], [2, 1], [3, 4], [4, 3]]
    refute Dominoes.chain?(dominoes)
  end

  def test_disconnected_single_isolated
    skip
    dominoes = [[1, 2], [2, 3], [3, 1], [4, 4]]
    refute Dominoes.chain?(dominoes)
  end

  def test_need_backtrack
    skip
    dominoes = [[1, 2], [2, 3], [3, 1], [2, 4], [2, 4]]
    assert Dominoes.chain?(dominoes)
  end

  def test_separate_loops
    skip
    dominoes = [[1, 2], [2, 3], [3, 1], [1, 1], [2, 2], [3, 3]]
    assert Dominoes.chain?(dominoes)
  end

  def test_nine_elements
    skip
    dominoes = [[1, 2], [5, 3], [3, 1], [1, 2], [2, 4], [1, 6], [2, 3], [3, 4], [5, 6]]
    assert Dominoes.chain?(dominoes)
  end
end
=begin
Write your code for the 'Dominoes' exercise in this file. Make the tests in
`dominoes_test.rb` pass.

To get started with TDD, see the `README.md` file in your
`ruby/dominoes` directory.
=end

class Dominoes
   
    def self.chain?(dominoes)
        @dominoes = dominoes

        return false if dominoes.length == 1 &&  dominoes[0][0] != dominoes[0][1]

        if dominoes.empty? || dominoes.nil? || dominoes.size == 1
            return true
        else
        permute_dominoes
        end
    end
    
    def self.permute_dominoes
        dominoes_array = []
        dominoes_array = @dominoes.permutation.to_a
        x = 0
        y = 1
        dominoes_array.each.with_index do |element, i|
            if dominoes_array.first.first == dominoes_array.last[1] && element[x][1] == element[y][0]
                return true
                x += 1
                y += 1
            else
                return false
            end
        end
    end
end

Community comments

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

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

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?