旋转链表.py

# 给定一个链表，旋转链表，将链表每个节点向右移动 k 个位置，其中 k 是非负数。
#
# 示例 1:
#
# 输入: 1->2->3->4->5->NULL, k = 2
# 输出: 4->5->1->2->3->NULL
# 解释:
# 向右旋转 1 步: 5->1->2->3->4->NULL
# 向右旋转 2 步: 4->5->1->2->3->NULL

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def rotateRight(self, head: ListNode, k: int) -> ListNode:
        if not head: return None
        if not head.next: return head
        old_tail = head
        n = 1
        while old_tail.next:
            old_tail = old_tail.next
            n += 1
        old_tail.next = head

        new_tail = head
        for i in range(n - k % n - 1):
            new_tail = new_tail.next
        new_head = new_tail.next

        new_tail.next = None
        return new_head