Python Program To Delete Alternate Nodes Of A Linked List

# Python3 program to remove alternate 
# nodes of a linked list 
import math 

# A linked list node 
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
        
# Deletes alternate nodes 
# of a list starting with head 
def deleteAlt(head): 
    if (head == None):
        return

    # Initialize prev and node to 
    # be deleted 
    prev = head 
    now = head.next

    while (prev != None and 
           now != None): 
        
        # Change next link of previous
        # node 
        prev.next = now.next

        # Free memory 
        now = None

        # Update prev and node 
        prev = prev.next
        if (prev != None): 
            now = prev.next
    
# UTILITY FUNCTIONS TO TEST 
# fun1() and fun2() 
# Given a reference (pointer to pointer) 
# to the head of a list and an , push a 
# new node on the front of the list. 
def push(head_ref, new_data): 
    
    # Allocate node 
    new_node = Node(new_data)

    # Put in the data 
    new_node.data = new_data 

    # Link the old list of the 
    # new node 
    new_node.next = head_ref 

    # Move the head to point to the 
    # new node 
    head_ref = new_node 
    return head_ref

# Function to print nodes in a 
# given linked list 
def printList(node): 
    while (node != None): 
        print(node.data, end = " ") 
        node = node.next
    
# Driver code 
if __name__=='__main__': 
    
    # Start with the empty list 
    head = None

    # Using head=push() to construct 
    # list 1.2.3.4.5 
    head = push(head, 5) 
    head = push(head, 4) 
    head = push(head, 3) 
    head = push(head, 2) 
    head = push(head, 1) 

    print("List before calling deleteAlt() ")
    printList(head) 

    deleteAlt(head) 

    print("List after calling deleteAlt() ") 
    printList(head) 
# This code is contributed by Srathore

# Deletes alternate nodes of a list 
# starting with head 
def deleteAlt(head): 
    if (head == None): 
        return

    node = head.next

    if (node == None): 
        return

    # Change the next link of head 
    head.next = node.next

    # Free memory allocated for node 
    free(node) 

    # Recursively call for the new 
    # next of head 
    deleteAlt(head.next) 
# This code is contributed by Srathore