倒数第K个结点

typedef  struct Lnode{
    int data;
    struct Lnode *next;
}Lnode,*Link; 
Link fi(Link head,int k){
    Link fa = head;
    Link sl = head;
    while(k>0&&fa!=null){
        fa = fa->next;
        k--;
    }
    if(k>0) //链表长度不足k
    else{
        while(fa!=null){
            fa = fa->next;
            sl = sl->next;
        }
        return sl;
    } 
}