203. Remove Linked List Elements

1.Question

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
2.Code

/**
* 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) {
while(head && head->val == val) head = head->next;
ListNode* pre = head;
while(pre && pre->next)
{
if(pre->next->val == val) pre->next = pre->next->next;
else pre = pre->next;
}
return head;
}
};

3.Note

a. 题目不难。这里想note的是，为了避免head->val 的head 或者pre->next 的pre 为NULL，在其前面加上"head
&& "或"pre &&"。这样方便把链表为空的情况考虑进来。