86 class Solution {    public ListNode partition(ListNode head, int x) {        ListNode lowheader=new ListNode(0);        ListNode low=lowheader;        ListNode highheader=new ListNode(0);        ListNode high=highheader;        while(head!=null){            if(head.val

 148

class Solution {    public ListNode sortList(ListNode head) {        while(head==null||head.next==null){            return head;        }        ListNode fast=head,low=head;        ListNode pre=null;        while(fast!=null&&fast.next!=null){            pre=low;            low=low.next;            fast=fast.next.next;        }        pre.next=null;        ListNode left=sortList(head);        ListNode right=sortList(low);        ListNode dummy=new ListNode(0);        ListNode curr=dummy;        while(left!=null&&right!=null){            if(left.val