use a singly linked list create a stack python
'''Python supports automatic garbage collection so deallocation of memory is done implicitly. However to force it to deallocate each node after use, add the following code: import gc #added at the start of program gc.collect() #to be added wherever memory is to be deallocated ''' class Node: # Class to create nodes of linked list # constructor initializes node automatically def __init__(self,data): self.data = data self.next = None class Stack: # head is default NULL def __init__(self): self.head = None # Checks if stack is empty def isempty(self): if self.head == None: return True else: return False # Method to add data to the stack # adds to the start of the stack def push(self,data): if self.head == None: self.head=Node(data) else: newnode = Node(data) newnode.next = self.head self.head = newnode # Remove element that is the current head (start of the stack) def pop(self): if self.isempty(): return None else: # Removes the head node and makes #the preceeding one the new head poppednode = self.head self.head = self.head.next poppednode.next = None return poppednode.data # Returns the head node data def peek(self): if self.isempty(): return None else: return self.head.data # Prints out the stack def display(self): iternode = self.head if self.isempty(): print("Stack Underflow") else: while(iternode != None): print(iternode.data,"->",end = " ") iternode = iternode.next return # Driver code MyStack = Stack() MyStack.push(11) MyStack.push(22) MyStack.push(33) MyStack.push(44) # Display stack elements MyStack.display() # Print top element of stack print("\nTop element is ",MyStack.peek()) # Delete top elements of stack MyStack.pop() MyStack.pop() # Display stack elements MyStack.display() # Print top element of stack print("\nTop element is ", MyStack.peek()) # This code is contributed by Mathew George
