Reorder List 

 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* cut(ListNode *head){
12         int count=0;
13         ListNode *temp=head;
14         while(temp!=NULL)
15         {
16             ++count;
17             temp=temp->next;
18         }
19         ListNode *lastHead=head;
20         for(int i=0;i<(count+1)/2;i++)
21         {
22             lastHead=lastHead->next;
23         }
24         ListNode *p,*q;
25         if(lastHead!=NULL&&lastHead->next!=NULL&&lastHead->next->next!=NULL)
26         {
27             p=lastHead;
28             q=lastHead->next;
29             lastHead->next=NULL;
30             ListNode *tempcut=q->next;
31             while(tempcut!=NULL)
32             {                
33                 q->next=p;
34                 p=q;
35                 q=tempcut;
36                 tempcut=tempcut->next;
37             }
38             q->next=p;
39             ListNode *last=q;
40             return last;
41         }
42         else if(lastHead->next==NULL)
43         {
44             lastHead->next=NULL;//应该把尾节点的next赋为空
45             return lastHead;
46         }
47         else if(lastHead->next->next==NULL)
48         {
49             p=lastHead;
50             lastHead=lastHead->next;
51             lastHead->next=p;
52             p->next=NULL;//应该把尾节点的next赋为空
53             return lastHead;
54         }
55     }
56     void reorderList(ListNode *head) {
57        if(head==NULL||head->next==NULL||head->next->next==NULL)
58            return;
59        else
60        {
61            ListNode *last=cut(head);
62            ListNode *p,*q;
63            p=head->next;
64            q=last->next;
65                while(p!=NULL&&q!=NULL)
66                {
67                    head->next=last;
68                    last->next=p;
69                    head=p;
70                    last=q;
71                    p=p->next;
72                    q=q->next;
73                }
74                head->next=last;
75                last->next=p;
76                p->next=NULL;//应该把尾节点的next赋为空
77        }
78     }
79 };
View Code

由于没给尾节点赋空值导致各种错误。

posted @ 2013-12-14 21:25  蓝兔子  阅读(143)  评论(0)  编辑  收藏  举报