Python Program For Reversing A Linked List In Groups Of Given Size - Set 1

# Python program to reverse a 
# linked list in group of given size

# Node class
class Node:

    # Constructor to initialize the 
    # node object
    def __init__(self, data):
        self.data = data
        self.next = None


class LinkedList:

    # Function to initialize head
    def __init__(self):
        self.head = None

    def reverse(self, head, k):      
        if head == None:
          return None
        current = head
        next = None
        prev = None
        count = 0

        # Reverse first k nodes of the linked list
        while(current is not None and 
              count < k):
            next = current.next
            current.next = prev
            prev = current
            current = next
            count += 1

        # next is now a pointer to (k+1)th node
        # recursively call for the list starting
        # from current. And make rest of the list as
        # next of first node
        if next is not None:
            head.next = self.reverse(next, k)

        # prev is new head of the input list
        return prev

    # Function to insert a new node at 
    # the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    # Utility function to print the 
    # Linked List
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next

# Driver code
llist = LinkedList()
llist.push(9)
llist.push(8)
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(3)
llist.push(2)
llist.push(1)

print "Given linked list"
llist.printList()
llist.head = llist.reverse(llist.head, 3)

print "Reversed Linked list"
llist.printList()
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)