Add Stack data structure: simple stack operations

data_structures/stacks/stack.rb

@@ -0,0 +1,76 @@
+# 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(stack, limit)
+    @stack = []
+    @limit = limit
+  end
+
+  attr_accessor :stack, :limit
+
+  def push(item)
+    if stack.count < limit
+      stack << item
+    else
+      raise StackOverflowError
+    end
+  end
+
+  def pop
+    stack.pop
+  end
+
+  def peek
+    stack.last
+  end
+
+  def is_empty?
+    stack.count == 0
+  end
+
+  def is_full
+    stack.count == limit
+  end
+
+  def size
+    stack.count
+  end
+
+  def contains?(item)
+    stack.include?(item)
+  end
+end
+
+stack = Stack.new([], 10)
+
+puts stack.is_empty?
+# => true
+
+stack.push(3)
+stack.push(5)
+stack.push(7)
+stack.push(9)
+
+puts stack.is_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>