08_RotateAList.py

# Question link - https://leetcode.com/problems/rotate-list/description/?envType=study-plan-v2&envId=top-interview-150

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def rotateRight(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
        length ,tail = 1, head

        # If empty 
        if (head is None or k == 0):
            return head
        
        # Length of LL
        while tail.next is not None:
            length += 1
            tail = tail.next

        # If k is equivalent to length 
        if (k % length == 0):
            return head
        
        k = k % length
        tail.next = head

        newLastNode = self.findLastNode(head , length - k)
        head = newLastNode.next
        newLastNode.next = None
        return head

    def findLastNode(self, temp , k):
        count = 1
        while temp is not None:
            if count == k:
                return temp
            count += 1
            temp = temp.next
        return temp