python | #删除链表的倒数第n个节点#

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#
# 
# @param head ListNode类 
# @param n int整型 
# @return ListNode类
#
class Solution:
    def removeNthFromEnd(self , head , n ):
        # write code here

        #防止head为空
        if head is None or n ==0:
            return head
        #链表只有一个节点的情况
        if head.next is None :
            if  n == 1:
                return None
            if n==0:
                return head
        #保存链表头
        head_r = head
        #计算列表长度
        l = 0
        while head:
            l+=1
            head = head.next
        #重新开始遍历
        head = head_r
        #找到倒数n+1个节点，并删除它的下一个节点
        if l==n:
            return head_r.next
        for i in range(l-n-1):
            head = head.next
        head.next = head.next.next
        return head_r