[LintCode] Insertion Sort List

Sort a linked list using insertion sort.
Example
Given 1->3->2->0->null, return 0->1->2->3->null.
 1 /**
 2  * Definition for ListNode.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int val) {
 7  *         this.val = val;
 8  *         this.next = null;
 9  *     }
10  * }
11  */ 
12 public class Solution {
13     /**
14      * @param head: The first node of linked list.
15      * @return: The head of linked list.
16      */
17     public ListNode insertionSortList(ListNode head) {
18         if(head == null || head.next == null){
19             return head;
20         }
21         ListNode dummy = new ListNode(0);
22         dummy.next = head;
23         ListNode sorted = dummy.next; ListNode prev = dummy;
24         ListNode unsorted = head.next;
25         sorted.next = null;
26         while(unsorted != null){
27             while(sorted != null && sorted.val <= unsorted.val){
28                 prev = sorted;
29                 sorted = sorted.next;    
30             }  
31             ListNode temp = unsorted.next;
32             unsorted.next = sorted;
33             prev.next = unsorted;
34             
35             unsorted = temp;
36             
37             prev = dummy;
38             sorted = dummy.next;
39         }
40         return dummy.next;
41     }
42 }