LeetCode 203. Remove Linked List Elements

删除一个链表中的特定值的元素，要注意删除后为空的情况

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        while(head && head->val == val)
            head = head->next;
        if(head == NULL ) return NULL;
        ListNode *tmp = head;
        while(tmp->next)
        {
            if(tmp->next->val == val)
                tmp->next = tmp->next->next;
            else tmp = tmp->next;
        }
        return head;
    }
};