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Rotate List

Question​

Given a linked list, rotate the list to the right by k places, where k is non-negative.

Example 1
Input: 1->2->3->4->5->NULL
K = 2 

Output: 4->5->1->2->3->NULL

Solution​

all//Rotate List.py


# 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, k):
        if not head:
            return head

        length = 0
        node = head
        while node:
            length += 1
            node = node.next

        k = k % length
        if k == 0:
            return head

        fast = slow = head
        for _ in range(k):
            fast = fast.next

        while fast.next:
            fast = fast.next
            slow = slow.next

        newHead = slow.next
        slow.next = None
        fast.next = head

        return newHead