How do pointers in linked lists relate to the lists themselves?

Question

I am working on leetcode #61, on rotating the linked list. I understand many of the solutions online, but I don't understand why the solution I came up with doesn't work. The logic seems simple: get two pointers, take one to the last node and the other one to the last-but-one node, then change the next nodes to the head and None respectively. Do this as many times as needed and return the resulting list. However, some nodes get lost in the way, and I can't figure out why this is happening. Here is my code:

class Solution:
    def rotateRight(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
        prev = head
        curr = prev.next
        while k > 0:
            while curr.next:
                prev = curr
                curr = curr.next
            curr.next = head
            prev.next = None
            
            k -= 1
            
        return curr

Can anybody explain to me where/what I am doing wrong?

Answer 1

First of all you have used nested loops, that will get you an n² time complexity. Which will be sufficient to give you a TLE and your answer will not be accepted.
Coming back to your solution, the problem here is that your head pointer is not updating(line number 9 of your code above) due to which, after each iteration of the outer while loop you will lose track of the node pointing your original header node, which will eventually make you loose the remaining nodes.