Stack

An ADT that contains a collection of elements, and follows the last in first out (LIFO) principle.¹

Properties

• only the most recently added element of the stack can be viewed
• returning the value of the last element added without modifying the collection is called peeking
• adding an element is called pushing
• removing the most recently added element is called *popping
• follows last in first out (LIFO) principle
  • the most recently added element will be the first element to be removed
• mutable length

Visual example

Signature

name: Stack
import: element, boolean
operators:
  newStack: -> Stack;
  push: Stack × element -> Stack;
  pop: Stack -> Stack;
  top: Stack -> element;
  isEmpty: Stack -> boolean;

Implementation

Python 3

class Stack:
    def __init__(self):
        self.Stack=[]
 
    def push(self,val):
        self.Stack.append(val)
        
    def pop(self):
        lengh=len(self.Stack)
        if lengh==0:
            return None
        else:
            return self.Stack.pop(lengh-1)
        
    def top(self):
        lengh=len(self.Stack)
        if lengh==0:
            return None
        else:
            return self.Stack[lengh-1] 
        
    def isEmpty(self):
        return (True if len(self.Stack) == 0 else False) 

Footnotes

1. https://en.wikipedia.org/wiki/Stack_(abstract_data_type) ↩