python实现链表中倒数第k个结点

题目描述

输入一个链表，输出该链表中倒数第k个结点

第一种实现：

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def FindKthToTail(self, head, k):
        # write code here
        l = []
        while head != None:
            l.append(head)
            head = head.next
        if k > len(l) or k < 1:
            return
        return l[-k]

 第二种实现：

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def FindKthToTail(self, head, k):
        # write code here
        if head == None or k == 0:
            return None
        pAhead = head
        pBehind = None
        for i in range(0,k-1):
            if pAhead.next != None:
                pAhead = pAhead.next
            else:
                return None
        pBehind = head
        while pAhead.next != None:
            pAhead = pAhead.next
            pBehind = pBehind.next
        return pBehind