ruby - linked-list

ruby/linked-list/README.md

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+# Linked List
+
+Implement a doubly linked list.
+
+Like an array, a linked list is a simple linear data structure. Several
+common data types can be implemented using linked lists, like queues,
+stacks, and associative arrays.
+
+A linked list is a collection of data elements called *nodes*. In a
+*singly linked list* each node holds a value and a link to the next node.
+In a *doubly linked list* each node also holds a link to the previous
+node.
+
+You will write an implementation of a doubly linked list. Implement a
+Node to hold a value and pointers to the next and previous nodes. Then
+implement a List which holds references to the first and last node and
+offers an array-like interface for adding and removing items:
+
+* `push` (*insert value at back*);
+* `pop` (*remove value at back*);
+* `shift` (*remove value at front*).
+* `unshift` (*insert value at front*);
+
+To keep your implementation simple, the tests will not cover error
+conditions. Specifically: `pop` or `shift` will never be called on an
+empty list.
+
+If you want to know more about linked lists, check [Wikipedia](https://en.wikipedia.org/wiki/Linked_list).
+
+* * * *
+
+For installation and learning resources, refer to the
+[Ruby resources page](http://exercism.io/languages/ruby/resources).
+
+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 linked_list_test.rb
+
+To include color from the command line:
+
+    ruby -r minitest/pride linked_list_test.rb
+
+
+## Source
+
+Classic computer science topic
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

ruby/linked-list/linked_list.rb

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+# Deque class
+class Deque
+  def initialize
+    @front = nil
+    @back = nil
+  end
+
+  def push(data)
+    element = Element.new(data)
+    element.prev = @back
+    @back.next = element if @back
+    @back = element
+    @front = element if @front.nil?
+  end
+
+  def pop
+    element = @back
+    @back = element.prev
+    @front = nil if @back.nil?
+    element.data
+  end
+
+  def unshift(data)
+    element = Element.new(data)
+    element.next = @front
+    @front.prev = element if @front
+    @front = element
+    @back = element if @back.nil?
+  end
+
+  def shift
+    element = @front
+    @front = element.next
+    @back = nil if @front.nil?
+    element.data
+  end
+end
+
+# Element class
+class Element
+  attr_accessor :data, :next, :prev
+
+  def initialize(data)
+    @data = data
+    @next = nil
+    @prev = nil
+  end
+end

ruby/linked-list/linked_list_test.rb

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+require 'minitest/autorun'
+require_relative 'linked_list'
+
+class DequeTest < Minitest::Test
+  def test_push_pop
+    # skip 
+    deque = Deque.new
+    deque.push(10)
+    deque.push(20)
+    assert_equal 20, deque.pop
+    assert_equal 10, deque.pop
+  end
+
+  def test_push_shift
+    # skip
+    deque = Deque.new
+    deque.push(10)
+    deque.push(20)
+    assert_equal 10, deque.shift
+    assert_equal 20, deque.shift
+  end
+
+  def test_unshift_shift
+    # skip
+    deque = Deque.new
+    deque.unshift(10)
+    deque.unshift(20)
+    assert_equal 20, deque.shift
+    assert_equal 10, deque.shift
+  end
+
+  def test_unshift_pop
+    # skip
+    deque = Deque.new
+    deque.unshift(10)
+    deque.unshift(20)
+    assert_equal 10, deque.pop
+    assert_equal 20, deque.pop
+  end
+
+  def test_example
+    # skip
+    deque = Deque.new
+    deque.push(10)
+    deque.push(20)
+    assert_equal 20, deque.pop
+    deque.push(30)
+    assert_equal 10, deque.shift
+    deque.unshift(40)
+    deque.push(50)
+    assert_equal 40, deque.shift
+    assert_equal 50, deque.pop
+    assert_equal 30, deque.shift
+  end
+
+  def test_pop_to_empty
+    # skip
+    deque = Deque.new
+    deque.push(10)
+    assert_equal 10, deque.pop
+    deque.push(20)
+    assert_equal 20, deque.shift
+  end
+
+  def test_shift_to_empty
+    # skip
+    deque = Deque.new
+    deque.unshift(10)
+    assert_equal 10, deque.shift
+    deque.unshift(20)
+    assert_equal 20, deque.pop
+  end
+end