【Leetcode】19—Remove Nth Node From End of List

一、题目描述

给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。
示例：

给定一个链表: 1->2->3->4->5, 和 n = 2.
当删除了倒数第二个节点后，链表变为 1->2->3->5.

说明：
给定的 n 保证是有效的。

二、代码实现

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        if head == None: return None
        dummy = ListNode(-1)
        dummy.next = head
        
        first = head
        second = head
        
        while n:
            first = first.next
            n = n - 1
            
        if first == None: return head.next
            
        while first.next:
            first = first.next
            second = second.next
            
        second.next = second.next.next
        return head