[LintCode] Insertion Sort List

Sort a linked list using insertion sort.

Example

Given 1->3->2->0->null, return 0->1->2->3->null.

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param head: The first node of linked list.
     * @return: The head of linked list.
     */
    public ListNode insertionSortList(ListNode head) {
        if(head == null || head.next == null){
            return head;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode sorted = dummy.next; ListNode prev = dummy;
        ListNode unsorted = head.next;
        sorted.next = null;
        while(unsorted != null){
            while(sorted != null && sorted.val <= unsorted.val){
                prev = sorted;
                sorted = sorted.next;    
            }  
            ListNode temp = unsorted.next;
            unsorted.next = sorted;
            prev.next = unsorted;
            
            unsorted = temp;
            
            prev = dummy;
            sorted = dummy.next;
        }
        return dummy.next;
    }
}