Leetcode每日一题：面试题02.02.kth-node-from-end-of-list-lcci（返回倒数第k个节点）_如果rgetkthnode()函数返回null,则输出无效,否则输出倒数第k个结点的数据。

思路：典型得快慢指针问题，快指针与慢指针中间隔着k-2个节点，那么同时++快慢指针，当快指针指向链表结尾节点时，慢指针指向倒数第k个节点；

struct ListNode
{
	int val;
	ListNode *next;
	ListNode(int x) : val(x), next(NULL) {}
};

int kthToLast(ListNode *head, int k)
{
	ListNode *left = head, *right = head;
	int count = 1;
	while (count < k)
	{
		right = right->next;
		count++;
	}
	while (right->next)
	{
		left = left->next;
		right = right->next;
	}
	return left->val;
}
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