一、題目描述

給定一個(gè)鏈表，刪除鏈表的倒數(shù)第 n 個(gè)節(jié)點(diǎn)，并且返回鏈表的頭結(jié)點(diǎn)。
示例：

給定一個(gè)鏈表: 1->2->3->4->5, 和 n = 2.
當(dāng)刪除了倒數(shù)第二個(gè)節(jié)點(diǎn)后，鏈表變?yōu)?1->2->3->5.

說明：
給定的 n 保證是有效的。

二、代碼實(shí)現(xiàn)

# 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