Insertion Sort List.java

/**
 * 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) {
        // write your code here
        if (head == null || head.next == null) {
            return head;
        }
        
        ListNode dummy = new ListNode(0);
        ListNode curr = head;
        
        while (curr != null) {
            ListNode pre = dummy;
            while (pre.next != null && pre.next.val < curr.val) {
                pre  = pre.next;
            }
            ListNode temp = curr.next;
            curr.next = pre.next;
            pre.next = curr;
            curr = temp;
        }
        
        return dummy.next;
    }
}