面试题 02.02. 返回倒数第 k 个节点

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
int kthToLast(ListNode *head, int k) {
    auto *dummy = new ListNode(-1);
    dummy->next = head;
    auto *l = dummy, *r = dummy;
    while (k--)
        r = r->next;

    while (r->next) {
        l=l->next;
        r=r->next;
    }
    return l->next->val;
}