/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* findKthToTail(ListNode* pListHead, int k) {
        int n = 0;
        for (auto a = pListHead; a; a=a->next) {
            ++n;
        }

        if (n < k) {
            return nullptr;
        }

        auto a = pListHead;
        for (int i = 0; i < n - k; ++i) {
            a = a->next;
        }
        return a;
    }
};