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61. Rotate List

Difficulty Topics

Description

Given the head of a linked list, rotate the list to the right by k places.

 

Example 1:

Input: head = [1,2,3,4,5], k = 2
Output: [4,5,1,2,3]

Example 2:

Input: head = [0,1,2], k = 4
Output: [2,0,1]

 

Constraints:

  • The number of nodes in the list is in the range [0, 500].
  • -100 <= Node.val <= 100
  • 0 <= k <= 2 * 109

Solution

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: Optional[ListNode], k: int) -> Optional[ListNode]:
        if not head or not head.next: return head

        length = 1
        curr = head

        while curr.next:
            length += 1
            curr = curr.next

        k %= length
        curr.next = head

        for _ in range(length - k):
            curr = curr.next

        head = curr.next
        curr.next = None

        return head