/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
    	int len=0;
        ListNode *p=pListHead;
        while(p!=NULL) {
            len++;//算出链表长度
            p=p->next;
        }
        if(k>len || k<0)	return NULL;//两种特殊情况
        int i=1; 　　//设置一个变量
        p=pListHead;//p重置为起点
        while(i<len-k+1) {//直到整数第len(list)-k个位置，进行最后一层循环，到达
            p=p->next;
            i++;
        }
        return p;
    }
};

class Solution {
public:
    ListNode* FindKthToTail(ListNode* p_head, unsigned int k)
    {//找到链表的倒数第K个节点
    //if(k==0)特殊处理,k小于链表长度，特殊处理
        if (k==0 || p_head == nullptr)
                return nullptr;
        ListNode* first = p_head;
        ListNode* second = p_head;
        for (int i = 0; i < k - 1; i++) {
            if(first->next== nullptr)	return nullptr;
            first = first->next;
        }
        while (first->next != nullptr)
        {
         first = first->next;
         second = second->next;
        }
        return second;
    }
};