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