Exercise_2.py

# Time Complexity :
#  Space Complexity :
#  Did this code successfully run on Leetcode :
#  Any problem you faced while coding this :

# implement stack using linked list
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None


class Stack:
    def __init__(self):
        self.head = None

    def push(self, data):
        if self.head == None:
            self.head = Node(data)
        else:
            new = Node(data)
            new.next = self.head
            self.head = new

    def pop(self):
        popped = self.head
        self.head = self.head.next
        popped.next = None
        return popped.data


a_stack = Stack()
while True:
    # Give input as string if getting an EOF error. Give input like "push 10" or "pop"
    print('push <value>')
    print('pop')
    print('quit')
    do = input('What would you like to do? ').split()
    # Give input as string if getting an EOF error. Give input like "push 10" or "pop"
    operation = do[0].strip().lower()
    if operation == 'push':
        a_stack.push(int(do[1]))
    elif operation == 'pop':
        popped = a_stack.pop()
        if popped is None:
            print('Stack is empty.')
        else:
            print('Popped value: ', int(popped))
    elif operation == 'quit':
        break