Abstract Data Types

In computer science, an abstract data type (ADT) is a mathematical model for data types.

An abstract data type is defined by its behavior (semantics) from the point of view of a user, of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations.

Stack

A stack is a Last-In First-Out (LIFO) abstract data structure

Attributes: A container that holds multiple data

Methods:

• Push → Adds Element to the top of the stack

• Pop → Removes the most recently added Element

• Peek → Look at the most recent element

Optional Methods:

• size() -> Returns the number of items in the Stack

• isEmpty() -> Returns True if the stack is empty

Stack & Complexity

All of stack operations are O(1) with Space complexity being O(n).

Stack Implementation in Python

class Stack:
    def __init__(self):
        self.__storage = []
    
    @property
    def length(self):
        return self.size()
    
    def push(self, value):
        self.__storage.append(value)
    
    def pop(self):
        return self.__storage.pop()
    
    def peek(self):
        return self.__storage[-1]
    
    def size(self):
        return len(self.__storage)
    
    def isEmpty(self):
        return len(self.__storage) == 0
    
    def __str__(self):
        if self.isEmpty():
            return "<>"
        else:
            output = ", ".join(map(str, self.__storage))
            return f"<{output}>"
    
    def __repr__(self):
        return f"<Stack Object @{str(hex(id(self)))}>"
# end of Stack