leetcode: 61. Rotate List

# Given a list, rotate the list to the right by k places, where k is non-negative.
#
# Example:
# Given 1->2->3->4->5->NULL and k = 2,
# return 4->5->1->2->3->NULL.

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution():
    def rotateRight(self, head, k):
        if not head:
            return None
        cur, n = head, 1
        while cur.next:
            cur, n = cur.next, n+1
        cur.next = head
        tail = cur = head
        for _ in range(n - k % n):
            tail, cur = cur, cur.next
        tail.next = None
        return cur


if __name__ == "__main__":
    head, head.next, head.next.next, head.next.next.next, head.next.next.next.next \
        = ListNode(1), ListNode(2), ListNode(3), ListNode(4), ListNode(5)
    print(Solution().rotateRight(head, 2))