Question

Write a code to implement a python stack class using linked list. use these operations

isEmpty   • push. • pop.   • peek. • size

Time and compare the performances ( this is optional but I would appreciate it)

Answer 1

# Node structure
class Node:
    def __init__(self, key, next=None):
        self.key = key
        self.next = next

# Main Stack structure
class Stack:

    def __init__(self):
        self.top = None
        self.count = 0

    # Utility function to add an element x in the stack
    def push(self, x):  # insert at the beginning

        # Allocate the new node in the heap
        node = Node(x)

        # check if stack  is full. Then inserting an element would
        # lead to stack overflow
        if node is None:
            print("Stack Overflow")
            return

        print("Pushing", x)

        # set the data in allocated node
        node.data = x

        # Set the .next pointer of the new node to point to the current
        # top node of the list
        node.next = self.top

        # update top pointer
        self.top = node
        self.count+=1
    def size(self):
        print("size of the current Stack is",self.count)
    # Utility function to check if the stack is empty or not
    def isEmpty(self):
        return self.top is None

    # Utility function to return top element in a stack
    def peek(self):

        # check for empty stack
        if not self.isEmpty():
            return self.top.data
        else:
            print("Stack is empty")
            return -1

    # Utility function to pop top element from the stack
    def pop(self):  # remove at the beginning

        # check for stack underflow
        if self.top is None:
            print("Stack Underflow")
            return

        print("Poping", self.peek())

        # update the top pointer to point to the next node
        self.top = self.top.next
        self.count-=1


if __name__ == '__main__':

    stack = Stack()

    stack.push(1)
    stack.push(2)
    stack.push(3)
    stack.size()
    print("Top element is", stack.peek())

    stack.pop()
    stack.size()
    stack.pop()
    stack.pop()

    if stack.isEmpty():
        print("Stack is empty")
    else:
        print("Stack is not empty")