203. Remove Linked List Elements（LeetCode）

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) {
        if(head==NULL)
            return head;
        else
        {  
            while(head&&head->val==val)
            {
                head=head->next;
            }
        }
        ListNode *p = head;
        ListNode *p1;
        while (p)
            {
                if (p->val == val)
                {
                    p = p->next;
                    p1->next=p;
                }
                else
                {
                    p1 = p;
                    p = p->next;    
                }
            }
        
        return head;
    }
};