题解 | #链表中倒数最后k个结点#

先找到倒数第k个结点所在的位置，然后进行长度判断。

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 *  ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
#include <cstdio>
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
        ListNode* dummy = new ListNode(0);
        dummy->next = pHead;
        ListNode* slow = dummy;
        ListNode* fast = dummy->next;
        int length = 0, k1 = k;

        while (k-- && fast != NULL) {
            length++;
            fast = fast->next;
        }
        while (fast != NULL) {
            slow = slow->next;
            fast = fast->next;
            length++;
        }
        if (length < k1) {
            return nullptr;
        }
        printf("%d", length);
        return slow->next;
    }
};