Leetcode-203 Remove Linked List Elements

#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

/**
 * 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* p=head;
        ListNode* pre=new ListNode();
        pre->next=head;
        ListNode* ret=pre;

        while(p!=NULL)
        {
            if(p->val==val)
            {
                pre->next=p->next;
            }
            else
            {
                pre=pre->next;
            }
            p=p->next;
        }
        return ret->next;
    }
};