Remove Linked List Elements

Description：

Remove all elements from a linked list of integers that have value val.

Example
Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6
Return: 1 --> 2 --> 3 --> 4 --> 5

Code1：

 1   ListNode* removeElements(ListNode* head, int val) {
 2         if (head==NULL)
 3         {
 4             return NULL;
 5         }
 6         
 7         //在链表两端分别插入头结点和尾结点
 8         ListNode* headNode = new ListNode(0);
 9         headNode->next = head;
10         
11         ListNode* q = headNode;
12         while (q->next)
13         {
14             q = q->next;
15         }
16         ListNode* tailNode = new ListNode(0);
17         q->next = tailNode;
18         
19         q = head;
20         ListNode* preNode = headNode;//指向被删结点的上一个结点
21         while (q!=tailNode)
22         {
23             if (q->val == val)
24             {
25                 preNode->next = q->next;
26                 delete q;
27                 q = preNode->next;
28             }
29             else
30             {
31                 q=q->next;
32                 preNode=preNode->next;
33             }
34         }
35         
36         if (headNode == tailNode)
37             return NULL;
38         else
39         {
40             preNode->next = NULL;
41             head = headNode->next;
42             delete headNode;
43             delete tailNode;
44             return head;
45         }
46     }

View Code

Code2:

 1   ListNode* removeElements(ListNode* head, int val) {
 2         if (head==NULL)
 3         {
 4             return NULL;
 5         }
 6 
 7         ListNode* q = head;
 8         ListNode* preNode = NULL;//指向被删结点的上一个结点
 9         while (q!=NULL)
10         {
11             if (q->val == val)
12             {
13                 if (q == head)
14                 {
15                     head = head->next;
16                     delete q;
17                     q = head;
18                 }
19                 else
20                 {
21                     preNode->next = q->next;
22                     delete q;
23                     q = preNode->next;
24                 }
25             }
26             else
27             {
28                 preNode = q;
29                 q=q->next;
30             }
31         }
32      return head;
33     }

View Code