剑指OFFER----面试题22. 链表中倒数第k个节点

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