Leetcode 61. Rotate List

https://leetcode.com/problems/rotate-list/

First we have to know the length of list, say n, then k = k % n. And then cut the list into two parts and put them back together.

Solution:

# T:O(n) S:O(1)
class Solution:
    # @param head, a ListNode
    # @param k, an integer
    # @return a ListNode
    def rotateRight(self, head, k):
        if k == 0 or head == None:
            return head
        dummy = ListNode(0)
        dummy.next, p, count = head, dummy, 0
        while p.next:
            p = p.next
            count += 1
        p.next = dummy.next
        step = count - ( k % count )
        for i in range(0, step):
            p = p.next
        head = p.next
        p.next = None
        return head

Run Time: 68 ms