题解 | #链表中倒数最后k个结点#

#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pHead ListNode类 
# @param k int整型 
# @return ListNode类
#
class Solution:
    def FindKthToTail(self , pHead: ListNode, k: int) -> ListNode:
        # write code here
        if not pHead:
            return None
        slow = fast = pHead    #典型快慢指针问题
        while fast and k>0:    #快指针先多走k步
            fast = fast.next
            k -= 1
        if k>0: return None
        while fast:            #快指针到头，慢指针位置即为倒数第k个节点
            slow = slow.next
            fast = fast.next
        return slow