A stack is a collection of objects that are inserted and removed using Last in First out Principle(LIFO). User can insert elements into the stack, and can only access or remove the recently inserted object on top of the stack. The main advantage of using LinkedList over array for implementing stack is the dynamic allocation of data whereas in the array, the size of the stack is restricted and there is a chance of stack overflow error when the size of the stack is exceeded the maximum size.
Stack Operations:
1. push() : Insert the element into Stack and assign the top pointer to the element.
2. pop() : Return top element from the Stack and move the top pointer to the second element of the Stack.
3. top() : Return the top element.
4. size() : Return the Size of the Stack.
5. isEmpty() : Return True if Stack is Empty else return False.
6. printstack() : Print all elements of the stack.
Below is the implementation of the above-mentioned stack operations using Doubly LinkedList in Python:
Implementation of Stack using Doubly Linked List
Python3
# A complete working Python program to demonstrate all # stack operations using a doubly linked list # Node class class Node:# Function to initialise the node object def __init__(self, data): self.data = data # Assign data self.next = None # Initialize next as null self.prev = None # Initialize prev as null # Stack class contains a Node objectclass Stack: # Function to initialize head def __init__(self): self.head = None # Function to add an element data in the stack def push(self, data): if self.head is None: self.head = Node(data) else: new_node = Node(data) self.head.prev = new_node new_node.next = self.head new_node.prev = None self.head = new_node # Function to pop top element and return the element from the stack def pop(self): if self.head is None: return None elif self.head.next is None: temp = self.head.data self.head = None return temp else: temp = self.head.data self.head = self.head.next self.head.prev = None return temp# Function to return top element in the stack def top(self): return self.head.data# Function to return the size of the stack def size(self): temp = self.head count = 0 while temp is not None: count = count + 1 temp = temp.next return count # Function to check if the stack is empty or not def isEmpty(self): if self.head is None: return True else: return False # Function to print the stack def printstack(self): print("stack elements are:") temp = self.head while temp is not None: print(temp.data, end ="->") temp = temp.next # Code execution starts here if __name__=='__main__': # Start with the empty stack stack = Stack()# Insert 4 at the beginning. So stack becomes 4->None print("Stack operations using Doubly LinkedList") stack.push(4)# Insert 5 at the beginning. So stack becomes 4->5->None stack.push(5)# Insert 6 at the beginning. So stack becomes 4->5->6->None stack.push(6)# Insert 7 at the beginning. So stack becomes 4->5->6->7->None stack.push(7)# Print the stack stack.printstack()# Print the top element print("\nTop element is ", stack.top())# Print the stack size print("Size of the stack is ", stack.size())# pop the top element stack.pop()# pop the top element stack.pop() # two elements are popped# Print the stack stack.printstack() # Print True if the stack is empty else False print("\nstack is empty:", stack.isEmpty())#This code is added by Suparna Raut |
Stack operations using Doubly LinkedList stack elements are: 7->6->5->4-> Top element is 7 Size of the stack is 4 stack elements are: 5->4-> stack is empty: False
Time Complexity for operations:
- Push(): O(1)
- pop(): O(1)
- top(): O(1)
- size(): O(N)
- isEmpty(): O(1)
- printStack(): O(N)
Auxiliary Space for operations:
- Push(): O(1)
- pop(): O(1)
- top(): O(1)
- size(): O(1)
- isEmpty(): O(1)
- printStack(): O(1)
