Update ruby-implementation.md

Author: davidlawrencer

stacks/ruby-implementation.md

@@ -0,0 +1,59 @@
+```ruby
+
+# Stack using array as underlying data collector 
+# we'll manipulate the element at the last index, since it supports O(1) operations
+
+class ArrayStack
+  def initialize
+    @list = []
+  end
+
+  def push(value)
+    @list.append(Node.new(value))
+  end
+  
+  def pop
+    @list.pop()
+  end
+
+  def top
+    @list.last
+  end
+
+  def isEmpty
+    @list.empty?
+  end
+end
+
+# Stack using LinkedList as underlying data collector 
+# we'll manipulate HEAD, since it supports O(1) operations
+
+class LLStack
+  def initialize
+    @list = LinkedList.new()
+  end
+
+  def push(value)
+    node = Node.new(value)
+    node.next = @list.head
+    @list.head = node
+  end
+  
+  def pop
+    newHead = @list.head.next
+    value = @list.head.value
+    @list.head = newHead
+    value
+  end
+  
+  def top
+    value = @list.head.value
+    value
+  end
+  
+  def is_empty?
+    @list.head.nil?
+  end
+end
+
+```