rotate-list.py

'''

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

Example 1:

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:

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


'''



# 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:

        # Approach one   前后指针，找到旋转到前面的部分链表
        if not head or not head.next or k == 0: return head
        fast =  slow = head
        num = 0
        while fast:
            fast = fast.next
            num += 1
        fast = head
        k = k % num
        if k == 0: return head

        while k:
            fast = fast.next
            k -= 1
        while fast.next:
            fast = fast.next
            slow = slow.next
        prev , res , slow.next = slow.next, slow.next, None
        while prev.next:
            prev = prev.next
        prev.next = head
        return res