题解 | #调整牛群顺序#

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @param n int整型 
# @return ListNode类
#
class Solution:
    def moveNthToEnd(self , head: ListNode, n: int) -> ListNode:
        # write code here
        res = ListNode(-1)
        res.next = head
        pre = res
        cur = head
        cnt = 0
        length = 0
        while cur:
            length+=1
            cur = cur.next
        cur = head 
        while cur:
            cnt += 1
            if cnt == (length-n+1):
                tmp = cur.val
                pre.next = cur.next
                cur = cur.next 
            else:
                pre = cur
                cur = cur.next
        last = ListNode(tmp)
        pre.next = last
        return res.next