61. 旋转链表

代码一：

class Solution(object):
    def rotateRight(self, head, k):
        """
        :type head: ListNode
        :type k: int
        :rtype: ListNode
        """
        tail = head
        res = []
        while tail:
            res.append(tail.val)
            tail = tail.next
        if len(res) == 0:
            return head
        k = k % len(res)
        while k > 0:
            temp = res.pop()
            res.insert(0, temp)
            k -= 1
        pre = node = ListNode(0)
        for i in range(len(res)):
            node.next = ListNode(0)
            node.next.val = res[i]
            node = node.next
        return pre.next

代码二：

class Solution(object):
    def rotateRight(self, head, k):
        """
        :type head: ListNode
        :type k: int
        :rtype: ListNode
        """
        if k==0:
            return head
        node = head
        len = 0
        while node:
            len += 1
            node = node.next
        if len<2 or len == k or k%len==0:
            return head
        k %= len
        cur, tail = head, head
        precur = ListNode(0)
        while k > 1 and tail.next:
            tail = tail.next
            k -= 1
        while tail.next:
            precur = cur
            cur = cur.next
            tail = tail.next
        tail.next = head
        precur.next = None
        head = cur
        return head