203. Remove Linked List Elements

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

Credits:

Special thanks to @mithmatt for adding this problem and creating all test cases.

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solution：

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {

ListNode *flag = new ListNode(0);
flag->next = head;
ListNode *pre = flag;
ListNode *cur = head;

while(cur!=NULL){
if(cur->val==val){
ListNode *tmpNode=cur;
pre->next = cur->next;
cur = cur->next;
delete tmpNode;
}
else{
pre = cur;
cur = cur->next;
}
}
head = flag->next;
delete flag;
return head;
}
};

自评：运行时间过长，主要由于释放了删除节点空间，但个人个人认为这部分操作是必要的