LeetCode 148. Sort List 

 1 class Solution {
 2 public:
 3     ListNode* getMid(ListNode* head){
 4     ListNode* slow = head, * fast = head;
 5     while(fast->next && fast->next->next){
 6         slow = slow->next;
 7         fast = fast->next->next;
 8         }
 9     return slow;
10     }
11     ListNode* merge(ListNode* head){
12         if(head->next == NULL) return head;
13         ListNode* mid = getMid(head);
14         ListNode* head2 = mid->next;
15         mid->next = NULL;
16         ListNode* new_head1 = merge(head);
17         ListNode* new_head2 = merge(head2);
18         
19         ListNode* res = new ListNode(0);
20         ListNode* resH = res;
21         while(new_head1 && new_head2){
22             if(new_head1->val < new_head2->val){
23                 res->next = new_head1;
24                 res = res->next;
25                 new_head1 = new_head1->next;
26             }
27             else{
28                 res->next = new_head2;
29                 res = res->next;
30                 new_head2 = new_head2->next;
31             }
32         }
33         while(new_head1){
34             res->next = new_head1;
35                 res = res->next;
36                 new_head1 = new_head1->next;
37         }
38         while(new_head2){
39             res->next = new_head2;
40             res = res->next;
41             new_head2 = new_head2->next;
42         }
43         return resH->next;
44     }
45     ListNode* sortList(ListNode* head) {
46         if(head == NULL) return head;
47         return merge(head);
48     }    
49 };

merge思想，应该还有更快算法，留坑。

posted @ 2016-03-14 19:26  co0oder  阅读(165)  评论(0)    收藏  举报