双指针

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode findKthToTail(ListNode pListHead, int k) {
        if (k == 0 || pListHead == null) return pListHead;
        int len = 0;
        ListNode cur = pListHead;
        while (cur != null) {
            cur = cur.next;
            len++;
        }
        if (k > len) return null;
        ListNode fast = pListHead, slow = pListHead;
        while (k-- > 0) {
            fast = fast.next;
        }
        while(fast != null) {
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}