Given a head to Linked List L, write a function to reverse the list taking k elements at a time. Assume k is a factor of the size of List.You need not have to create a new list. Just reverse the old one using head.
Question
Given a head to Linked List L, write a function to reverse the list taking k elements at a time. Assume k is a factor of the size of List.You need not have to create a new list. Just reverse the old one using head.
Solution
Sure, here is a Python solution for reversing a linked list in groups of k elements:
class Node:
def __init__(self, data):
self.data = data
self.next = None
def reverse(head, k):
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 = reverse(next, k)
# prev is new head of the input list
return prev
def push(head_ref, new_data):
new_node = Node(new_data)
new_node.next = head_ref
return new_node
def printList(node):
while(node != None):
print(node.data, end=" ")
node = node.next
print()
# Driver code
if __name__ == "__main__":
head = None
head = push(head, 9)
head = push(head, 8)
head = push(head, 7)
head = push(head, 6)
head = push(head, 5)
head = push(head, 4)
head = push(head, 3)
head = push(head, 2)
head = push(head, 1)
print("Given linked list")
printList(head)
head = reverse(head, 3)
print("Reversed Linked list")
printList(head)
This code first defines a Node class for the linked list. The reverse function is where the main logic happens. It reverses the first k nodes, then recursively calls itself on the rest of the list. The push function is used to add elements to the list, and printList is used to print the list. The driver code creates a list, prints it, reverses it in groups of 3, then prints the reversed list.
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