剑指offer--链表中倒数第k个结点

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindKthToTail(ListNode head,int k) {
        ListNode p = head;
        int len = 0;
        if (k < 0) {  
             System.out.println("k不可以为负数");  
             return null;  
        }  

        if (head == null) {  
            System.out.println("单链表为空");  
            return null;
        }  

        while(p != null){
            len++;
            p = p.next;
        }

        if ( k > len){
            System.out.print("单链表太短");
            return null;
        }else{
            k = len - k ;
            while(k > 0){
                head = head.next;
                k--;
            }
            return head;
        }
    }
}

struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};
class Solution {
public:
    ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
        if (k <= 0 || pListHead == NULL){
            return NULL;
        }
        ListNode* p1 = pListHead;
        ListNode* p2 = pListHead;
        for(int i = 0 ; i != k ; i++){
            if(p1 == NULL){
                return NULL; 
            }else{
                p1 = p1->next;  
            }
        }
        while(p1){
            p1 = p1->next;
            p2 = p2->next;
        }
        return p2;
    }
};