Stacks

inserting an Image

Analyzing the Array - Based Stack Implementation

Operation	Running Time
push(e)	O (1)
pop()	O (1)
peak()	O (1)
is_empty()	O (1)
len()	O (1)

Implementing a Stack using an Array:

Pros: Easy Cons: Not dynamic

Code:

class Stack():

def __init__(self):
    self.items = []

def push(self, item):
    self.items.append(item)				

def pop(self):
    return self.items.pop()

def is_empty(self):
    return self.items == []

def peek(self):
    if not self.is_empty():
        return self.items[-1]

def get_stack(self):
    return self.items

def print_stack(self):
    
    for element in self.items:
        print(element)



stack_practice = Stack()

stack_practice.push('A')
stack_practice.push('B')
stack_practice.push('D')
stack_practice.push('C')
stack_practice.push('J')
print("Stack Before Popping: ")
stack_practice.print_stack()
print("\n")
stack_practice.pop()
print("Stack After Popping: ")
stack_practice.print_stack()

Implementing a Stack using an Linked List:

Code:

class Node: 

    def __init__(self, data): 
        self.data = data  
        self.next = None

class Stack: 

    def __init__(self): 
        self.head = None

    def isEmpty(self): 
        return True if self.head is None else  False 

    def push(self, data): 

        new_node = Node(data)

        new_node = self.head

        self.head = new_node

        print("Push onto stack", data)


    def pop(self): 
        if (self.isEmpty()): 
            return float("-inf") 
        temp = self.head
        self.head = self.head.next 
        popped = temp.data 
        return popped 

    def peek(self): 
        if self.isEmpty(): 
            return float("-inf") 
        return self.head.data 
        