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Python3 Program to Rotate the sub-list of a linked list from position M to N to the right by K places

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  • Last Updated : 18 May, 2022

Given a linked list and two positions ‘m’ and ‘n’. The task is to rotate the sublist from position m to n, to the right by k places.

Examples:

Input: list = 1->2->3->4->5->6, m = 2, n = 5, k = 2
Output: 1->4->5->2->3->6
Rotate the sublist 2 3 4 5 towards right 2 times
then the modified list are: 1 4 5 2 3 6

Input: list = 20->45->32->34->22->28, m = 3, n = 6, k = 3
Output: 20->45->34->22->28->32
Rotate the sublist 32 34 22 28 towards right 3 times
then the modified list are: 20 45 34 22 28 32

Approach: For rotating the given sublist that extends from m to n element, move the list from (n-k+1)th to nth node to starting of sub-list to finish the rotation.
If k is greater than size of sublist then we will take its modulo with size of sublist. So traverse through list using a pointer and a counter and we will save (m-1)th node and later make it point to (n-k+1)th node and hence bring (n-k+1)th node to the start(front) of sublist.
Similarly we will save mth node and later make nth node point to it. And for keeping rest of list intact we will make (n-k)th node point to next node of n (maybe NULL). And finally we will get the k times right rotated sublist.

Below is the implementation of the above approach:

Python3




# Python3 implementation of the above approach
import math
  
# Definition of node of linkedlist
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
# This function take head pointer of list, 
# start and end points of sublist that is 
# to be rotated and the number k and
# rotate the sublist to right by k places.
def rotateSubList(A, m, n, k):
    size = n - m + 1
  
    # If k is greater than size of sublist then 
    # we will take its modulo with size of sublist
    if (k > size):
        k = k % size
      
    # If k is zero or k is equal to size or k is
    # a multiple of size of sublist then list 
    # remains intact
    if (k == 0 or k == size):
        head = A
        while (head != None):
            print(head.data)
            head = head.next
          
        return
      
    link = None # m-th node
    if (m == 1) :
        link = A
      
    # This loop will traverse all node till
    # end node of sublist. 
    c = A # Current traversed node
    count = 0 # Count of traversed nodes
    end = None
    pre = None # Previous of m-th node
    while (c != None) :
        count = count + 1
  
        # We will save (m-1)th node and later
        # make it point to (n-k+1)th node
        if (count == m - 1) :
            pre = c
            link = c.next
          
        if (count == n - k) :
            if (m == 1) :
                end = c
                A = c.next
              
            else :
                end = c
  
                # That is how we bring (n-k+1)th
                # node to front of sublist.
                pre.next = c.next
              
        # This keeps rest part of list intact.
        if (count == n) :
            d = c.next
            c.next = link
            end.next = d
            head = A
            while (head != None) :
                print(head.data, end = " ")
                head = head.next
              
            return
          
        c = c.next
      
# Function for creating and linking new nodes
def push(head, val):
    new_node = Node(val)
    new_node.data = val
    new_node.next = head
    head = new_node
    return head
  
# Driver code
if __name__=='__main__'
    head = None
    head = push(head, 70)
    head = push(head, 60)
    head = push(head, 50)
    head = push(head, 40)
    head = push(head, 30)
    head = push(head, 20)
    head = push(head, 10)
    tmp = head
    print("Given List: ", end = "")
    while (tmp != None) :
        print(tmp.data, end = " ")
        tmp = tmp.next
      
    print()
  
    m = 3
    n = 6
    k = 2 
    print("After rotation of sublist: ", end = "")
    rotateSubList(head, m, n, k)
  
# This code is contributed by Srathore

Output:

Given List: 10 20 30 40 50 60 70 
After rotation of sublist: 10 20 50 60 30 40 70

Please refer complete article on Rotate the sub-list of a linked list from position M to N to the right by K places for more details!


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