Merge pull request #70 from vbrazo/add-stack-data-structure-example

Stack data structure: simple stack operations

DIRECTORY.md

@@ -13,6 +13,8 @@
   * Linked Lists
     * [Double List](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/linked_lists/double_list.rb)
     * [Single List](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/linked_lists/single_list.rb)
+  * Stacks
+    * [Stack](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/stacks/stack.rb)
   * Tries
     * [Trie](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/tries/trie.rb)
 

data_structures/stacks/stack.rb

@@ -0,0 +1,87 @@
+# A stack is an abstract data type that serves as a collection of
+# elements with two principal operations: push() and pop(). push() adds an
+# element to the top of the stack, and pop() removes an element from the top
+# of a stack. The order in which elements come off of a stack are
+# Last In, First Out (LIFO)
+
+class StackOverflowError < StandardError; end
+
+class Stack
+  def initialize(limit, stack = [])
+    @stack = stack
+    @limit = limit
+  end
+
+  attr_accessor :stack, :limit
+
+  def push(item)
+    raise StackOverflowError unless stack.count < limit
+
+    stack << item
+  end
+
+  def pop
+    stack.pop
+  end
+
+  def peek
+    stack.last
+  end
+
+  def empty?
+    stack.count.zero?
+  end
+
+  def full?
+    stack.count == limit
+  end
+
+  def size
+    stack.count
+  end
+
+  def contains?(item)
+    stack.include?(item)
+  end
+end
+
+stack = Stack.new(10, [])
+
+puts stack.empty?
+# => true
+
+stack.push(3)
+stack.push(5)
+stack.push(7)
+stack.push(9)
+
+puts stack.full?
+# => false
+
+puts stack.contains?(5)
+# => true
+
+puts stack.pop
+# => 9
+
+puts stack.peek
+# => 7
+
+puts stack.size
+# => 3
+
+puts stack.inspect
+# => #<Stack:0x00007fceed83eb40 @stack=[3, 5, 7], @limit=10>
+
+stack.push(13)
+stack.push(15)
+stack.push(17)
+stack.push(19)
+stack.push(23)
+stack.push(25)
+stack.push(27)
+# At this point, the stack is full
+
+stack.push(29)
+# => data_structures/stacks/stack.rb:18:in `push': StackOverflowError (StackOverflowError)
+# from data_structures/stacks/stack.rb:83:in `<main>'