LeetCode刷题笔记——19. 删除链表的倒数第N个节点

难度：中等

一、题目描述：

二、解题分析：
1、解析

  这道题本质上和《剑指Offer》刷题笔记——面试题22. 链表中倒数第k个节点是一样的。都可以用单指针两次遍历或者双指针一次遍历解决。

2、代码实现

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        if head is None:
            return
        cur = head
        length = 1
        while cur.next:
            length += 1
            cur = cur.next
        if length == n:
            head = head.next
            return head
        count = 1
        cur = head
        pre = cur
        while length-count+1 != n:
            count += 1
            pre = cur
            cur = cur.next
        pre.next = cur.next
        return head