剑指offer【22】求链表倒数第K个结点

class listNode:
    def __init__(self,elem,next_=None):
        self.elem=elem
        self.next_=next_

def findk(head,k):
    if k==0 or head==None:
        p=q=head
        i=0
        j=0
        while p.next_ != None:
            i+=1
            p=p.next_
            if i>=k:
                q=q.next_
        if k>i:
            return None

        return q
    
a=listNode(3,None)
b=listNode(4,a)
c=listNode(5,b)
d=listNode(6,c)