Stack

Stack (Data Structure)

Stack is a linear data structure that follows the Last In First Out (LIFO) principle. The elements are inserted and removed from the same end.

Operations

Push: Insert an element at the top.
Pop: Remove an element from the top.
Peek: Get the top element.

Example

class Stack:
    def __init__(self):
        self.stack = []
 
    def push(self, item):
        self.stack.append(item)
 
    def pop(self):
        if len(self.stack) == 0:
            return None
        return self.stack.pop()
 
    def peek(self):
        if len(self.stack) == 0:
            return None
        return self.stack[-1]
 
s = Stack()
s.push(1)
s.push(2)
s.push(3)
 
print(s.pop()) # 3
print(s.peek()) # 2

Built-in Stack in Python

Python provides a built-in list that can be used as a stack data structure. It provides a more efficient way to implement a stack.

stack = []
 
stack.append('a')
stack.append('b')
stack.append('c')
 
stack.pop() # removes last element
 
print(stack)  # ['a', 'b']

Operations complexity (Time Complexity)

Push: O(1)
Pop: O(1)
Peek: O(1)

Design Patterns Queue