61. 旋转链表

给你一个链表的头节点 head ，旋转链表，将链表每个节点向右移动 k 个位置。

示例 1：

输入：head = [1,2,3,4,5], k = 2
输出：[4,5,1,2,3]

示例 2：

输入：head = [0,1,2], k = 4
输出：[2,0,1]

提示：

• 链表中节点的数目在范围 [0, 500] 内
• -100 <= Node.val <= 100
• 0 <= k <= 2 * 10^9

Python 解答：

# 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: ListNode, k: int) -> ListNode:
        if not head or not k:
            return head
        p = head
        lens = 0
        pre, seq = None, None
        while p:
            lens += 1
            seq = p
            p = p.next
        k = lens - k % lens
        if k == lens:
            return head
        p = head
        while k > 0:
            pre = p
            p = p.next
            k -= 1
        pre.next = None
        seq.next = head
        return p