题目

思路

左边一个往进插数字 ，右边一个往进插数字 ，整个队列都完了以后让左边的尾指针指向右边的头指针，将两个链表连起来再返回即可。

代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    
    public ListNode partition(ListNode head, int x) {
        //head指的是当前节点
        //next用来记住当前节点的下一个 防止丢失

       ListNode leftHead = null,leftTail = null;
       ListNode rightHead = null,rightTail = null;
       ListNode next = null;
//在当前list上进行操作，不是新建，不存在浪费空间
        while(head != null){
            next = head.next;
            head.next = null;

            if(head.val < x){
                if(leftHead == null){
                    leftHead = head;
                }else{
                    leftTail.next = head;
                }
                leftTail = head;
            }else{
                if(rightHead == null){
                    rightHead = head;
                }else{
                    rightTail.next = head;
                }
                rightTail = head;
            }
            head = next;
        }
        if(leftHead == null){
            return rightHead;
        }
        leftTail.next = rightHead;
        return leftHead;
    }
}