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 == NULL)            return head;        ListNode* preNode = NULL;        ListNode* curNode = head;        while(curNode != NULL){            if(curNode->val == val){                if(preNode == NULL){                    head = curNode->next;                    curNode = curNode->next;                }else{                    preNode->next = curNode->next;                    curNode = curNode->next;                }            }else{                preNode = curNode;                curNode = curNode->next;            }        }        return head;    }};