/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* findKthToTail(ListNode* head, int k) {
        auto *q = head;
        int count = 0;
        for(auto p = head;p;p = p->next) 
            if(count < k) count++;
            else q = q->next;

        if(count < k) return nullptr;
        else    return q;
    }
};