[Leetcode] Insertion Sort List

Sort a linked list using insertion sort.

虽然算法很简单，但是链表操作起来实正是烦啊，特别要注意各种边界条件。

 1 /**

 2  * Definition for singly-linked list.

 3  * struct ListNode {

 4  *     int val;

 5  *     ListNode *next;

 6  *     ListNode(int x) : val(x), next(NULL) {}

 7  * };

 8  */

 9 class Solution {

10 public:

11     ListNode *insertionSortList(ListNode *head) {

12          if (head == NULL || head->next == NULL) {

13         return head;

14     }

15     ListNode *h = new ListNode(0);

16     h->next = head;

17     ListNode *p, *q, *tmp;

18     bool flag;

19     for (p = head; p->next != NULL;) {

20         flag = false;

21         for (q = h; q != p; q = q->next) {

22             if (p->next->val < q->next->val) {

23                 tmp = p->next;

24                 p->next = tmp->next;

25                 tmp->next = q->next;

26                 q->next = tmp;

27                 flag = true; break;

28             }

29         }

30         if (!flag) p = p->next;

31     }

32     head = h->next;

33     delete h; h = NULL;

34     return head;

35     }

36 };