【LeetCode】Partition List

小于x的所有节点串成一个链表

大于等于x的所有节点串成一个链表

再将两者拼接起来，注意要链表节点之间的断开和连接，不要死循环了

/**
 * 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) {
        if(head == null || head.next == null) return head;
        ListNode h1 = new ListNode(-1);
        h1.next = null;
        ListNode dummy1 = h1;
        ListNode h2 = new ListNode(-1);
        h2.next = null;
        ListNode dummy2 = h2;
        ListNode pre = null;
        while(head != null){
            pre = head;
            if(head.val < x){
                h1.next = head;
                h1 = h1.next;
            }
            else{
                h2.next = head;
                h2 = h2.next;
            }
            head = head.next;
            pre.next = null;
            
        }
        h1.next = dummy2.next;
        return dummy1.next;
    }
}