61. Rotate List

2019-05-12

61. Rotate List

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

Example 1:

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Input: 1->2->3->4->5->NULL, k = 2
Output: 4->5->1->2->3->NULL
Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL

Example 2:

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Input: 0->1->2->NULL, k = 4
Output: 2->0->1->NULL
Explanation:
rotate 1 steps to the right: 2->0->1->NULL
rotate 2 steps to the right: 1->2->0->NULL
rotate 3 steps to the right: 0->1->2->NULL
rotate 4 steps to the right: 2->0->1->NULL

Code：

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

class Solution(object):
    def rotateRight(self, head, k):
        n, pre, current = 0, None, head
        while current:
            pre, current = current, current.next
            n += 1

        if not n or not k % n:
            return head

        tail = head
        for _ in xrange(n - k % n - 1):
            tail = tail.next

        next, tail.next, pre.next = tail.next, None, head
        return next
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