[leetcode] Insert sort list

https://leetcode.com/problems/insertion-sort-list/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode insertionSortList(ListNode head) {
        if (head == null || head.next == null) {
			return head;
		}
		ListNode h = new ListNode(0), p = head, pre = h, q = head.next;
		h.next = head;
		p.next = null;
		while (q != null) {
			while (p != null && q.val >= p.val) {
				pre = p;
				p = p.next;
			}
			ListNode t = q.next;
			pre.next = q;
			q.next = p;
			q = t;
			pre = h;
			p = h.next;
		}
		return h.next;
    }
}