/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode partition(ListNode head, int x) {        ListNode leftDummy = new ListNode(0);        ListNode rightDummy = new ListNode(0);        ListNode left = leftDummy;        ListNode right = rightDummy;        while (head != null) {            if (head.val < x) {                left.next = head;                left = head;            } else {                right.next = head;                right = head;            }            head = head.next;        }        right.next = null;        left.next = rightDummy.next;        return leftDummy.next;    }}

这段代码不加right.next = null; 这句话就会报错

若不置空，right.next可能指向某个链表中已经存在的结点。