Remove Linked List Elements

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