题解 | #链表中倒数最后k个结点#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 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
     */
    ListNode* FindKthToTail(ListNode* pHead, int k) 
    {
        // write code here
        if (pHead == NULL)
        {
            return pHead;
        }

        int cnt = 0;
        ListNode * jilu = pHead;
        while (jilu != NULL)
        {
            jilu = jilu->next;
            cnt += 1;
        }
        //cout << cnt ;
        if (cnt < k)
        {
            return NULL;
        }

        ListNode * fast = pHead;
        for (int i = 0;i < k;i++)
        {
            fast = fast->next;
        }
        ListNode * slow = pHead;
        while (fast != NULL)
        {
            fast = fast->next;
            slow = slow->next;
        }
        return slow;
    }
};