leetcode 147. Insertion Sort List

 1 ListNode *insertionSortList(ListNode *head) 
 2     {
 3         ListNode *dummy = new ListNode(INT_MIN), *p, *q, *pre;
 4         dummy->next = head;
 5 
 6         pre = dummy;
 7         q = pre->next;
 8         while (q != NULL)
 9         {
10             p = dummy;
11             while (p->next != q)
12             {
13                 if (q->val < p->next->val)
14                 {
15                     pre->next = q->next;
16                     q->next = p->next;
17                     p->next = q;
18                     q = pre->next;
19                     break;
20                 }
21                 p = p->next;
22             }
23             if (p->next == q)
24             {
25                 pre = q;
26                 q = pre->next;
27             }
28         }
29         p = dummy->next;
30         delete dummy;
31         return p;
32     }