[LintCode]Remove Linked List Elements(C++)

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    /**
     * @param head a ListNode
     * @param val an integer
     * @return a ListNode
     */
    ListNode *removeElements(ListNode *head, int val) {
        // Write your code here
        ListNode **p = &head;
        while (*p) {
            if ((*p)->val == val) {
                if ((*p)->next == NULL){
                    delete *p;
                    *p = NULL;
                }else{
                    ListNode *x = *p;
                    *p = (*p)->next;
                    delete x;
                }
            }else
                p = &(*p)->next;
        }
        return head;
    }
};