题解 | #链表中倒数最后k个结点#

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
# 
# @param pHead ListNode类 
# @param k int整型 
# @return ListNode类
#
# 双指针法，先将右指针移动 k-1 步，然后再同时移动左指针和右指针，当右指针移动到最后一个节点时，输出左指针
class Solution:
    def FindKthToTail(self , pHead: ListNode, k: int) -> ListNode:
        if pHead == None:
            return None
        if k <= 0:
            return None

        l, r = pHead, pHead
        for i in range(k-1):
            r = r.next
            if r == None:
                return None
        
        while r.next != None:
            l = l.next
            r = r.next

        return l