删除链表中倒数K元素

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode removeNthFromEnd(ListNode head, int n) {        ListNode pa = head;        ListNode pb = head;        // 找到第n个结点        for (int i = 0; i < n && pa != null; i++) {            pa = pa.next;        }        if (pa == null) {            head = head.next;            return head;        }        // pb与pa相差n-1个结点        // 当pa.next为null，pb在倒数第n+1个位置        while (pa.next != null) {            pa = pa.next;            pb = pb.next;        }        pb.next = pb.next.next;//删除caozuo        return head;    }}