答案

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode partition(ListNode head, int x) {
        ListNode leftHead=new ListNode(0);
        ListNode rightHead=new ListNode(0);
        ListNode pLeft=leftHead;
        ListNode pRight=rightHead;
        for(ListNode p=head;p!=null;p=p.next)
        {
            if(p.val<x)
            {
                pLeft.next=p;
                pLeft=p;
            }
            else
            {
                pRight.next=p;
                pRight=p;
            }
        }
        pRight.next=null;
        pLeft.next=rightHead.next;
        return leftHead.next;
    }
}