leetcode86. 分隔链表

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

思路：分别创建两个链表保存两种节点，最后连起来即可。

/**
 * 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 before_head = new ListNode(0);
        ListNode before = before_head;
        ListNode after_head = new ListNode(0);
        ListNode after = after_head;
        while (head != null) {
            if (head.val < x) {
                before.next = head;
                before = before.next;
            } else {
                after.next = head;
                after = after.next;
            }
            head = head.next;
        }
        after.next = null;
        before.next = after_head.next;

        return before_head.next;
    }
}