InsertionSortList

/**
 * 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 insertionSortList(ListNode head) {
        if (head==null || head.next==null) 
            return head;
        
        ListNode dummy = new ListNode(0); 
        dummy.next = head;
        
        ListNode sortedTail = head;   //tail/end of sorted list
        while (sortedTail.next != null) 
        {
            if (sortedTail.val <= sortedTail.next.val) {
                sortedTail = sortedTail.next;
            } 
            else 
            {
                ListNode tmp = sortedTail.next;
                sortedTail.next = sortedTail.next.next;
                ListNode pre = dummy; // this pointer will iterate from head to sorted tail to find temp's position
                while (pre.next.val <= tmp.val)
                    pre = pre.next;
                tmp.next = pre.next;
                pre.next = tmp;
            }
        } 
        
        return dummy.next;
    
    }
}