给定一个链表和一个特定值 x，对链表进行分隔，使得所有小于 x 的节点都在大于或等于 x 的节点之前。
你应当保留两个分区中每个节点的初始相对位置。
示例:
输入: head = 1->4->3->2->5->2, x = 3
输出: 1->2->2->4->3->5
解：
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode partition(ListNode head, int x) {
ListNode dummy1 = new ListNode(0);
ListNode dummy2 = new ListNode(0);
ListNode curr1 = dummy1;
ListNode curr2 = dummy2;
while (head != null) {
if (head.val < x) {
curr1.next = head;
curr1 = curr1.next;
} else {
curr2.next = head;
curr2 = curr2.next;
}
head = head.next;
}
curr2.next = null;
curr1.next = dummy2.next;
return dummy1.next;
}
}
