Sort Linked List Already Sorted Using Absolute Values

给一个按照绝对值排序的链表, 求按照数字排序的链表.

这题就是先拆分成pos和neg两个链表, 然后如果neg是空的, 返回pos, 如果不是, 翻转neg后连上pos再返回.

/**
 * 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 sortLinkedList(ListNode head) {
        ListNode neg = new ListNode();
        ListNode pos = new ListNode();
        ListNode nh = neg;
        ListNode ph = pos;
        ListNode p = head;
        while(p != null){
            if(p.val >= 0){
                ph.next = new ListNode(p.val);
                ph = ph.next;
            }
            else
            {
                nh.next = new ListNode(p.val);
                nh = nh.next;
            }
            p = p.next;
        }
        if(neg.next == null)
            return pos.next;
        ListNode th = rev(neg.next);
        ListNode d = th;
        while(d.next != null)
            d = d.next;
        d.next = pos.next;
        return th;
    }
    private ListNode rev(ListNode head) {
        ListNode newHead = null;
        while(head != null){
            ListNode next = head.next;
            head.next = newHead;
            newHead = head;
            head = next;
        }
        return newHead;
    }
}