Python Program For Reversing A Linked List In Groups Of Given Size- Set 2
Last Updated :
18 May, 2022
Given a linked list, write a function to reverse every k nodes (where k is an input to the function).Â
Examples:
Input: 1->2->3->4->5->6->7->8->NULL and k = 3
Output: 3->2->1->6->5->4->8->7->NULL.
Input: 1->2->3->4->5->6->7->8->NULL and k = 5
Output: 5->4->3->2->1->8->7->6->NULL.
We have already discussed its solution in below postÂ
Reverse a Linked List in groups of given size | Set 1
In this post, we have used a stack which will store the nodes of the given linked list. Firstly, push the k elements of the linked list in the stack. Now pop elements one by one and keep track of the previously popped node. Point the next pointer of prev node to top element of stack. Repeat this process, until NULL is reached.
This algorithm uses O(k) extra space.
Python3
class Node( object ):
__slots__ = 'data' , 'next'
def __init__( self , data = None ,
next = None ):
self .data = data
self . next = next
def __repr__( self ):
return repr ( self .data)
class LinkedList( object ):
def __init__( self ):
self .head = None
def __repr__( self ):
nodes = []
curr = self .head
while curr:
nodes.append( repr (curr))
curr = curr. next
return '[' + ', ' .join(nodes) + ']'
def prepend( self , data):
self .head = Node(data = data,
next = self .head)
def reverse( self , k = 1 ):
if self .head is None :
return
curr = self .head
prev = None
new_stack = []
while curr is not None :
val = 0
while curr is not None and val < k:
new_stack.append(curr.data)
curr = curr. next
val + = 1
while new_stack:
if prev is None :
prev = Node(new_stack.pop())
self .head = prev
else :
prev. next = Node(new_stack.pop())
prev = prev. next
prev. next = None
return self .head
llist = LinkedList()
llist.prepend( 9 )
llist.prepend( 8 )
llist.prepend( 7 )
llist.prepend( 6 )
llist.prepend( 5 )
llist.prepend( 4 )
llist.prepend( 3 )
llist.prepend( 2 )
llist.prepend( 1 )
print ( "Given linked list" )
print (llist)
llist.head = llist.reverse( 3 )
print ( "Reversed Linked list" )
print (llist)
|
Output:Â
Given Linked List
1 2 3 4 5 6 7 8 9
Reversed list
3 2 1 6 5 4 9 8 7
Please refer complete article on Reverse a Linked List in groups of given size | Set 2 for more details!
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