[leetcode] 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)
  {
    ListNode *pre_ptr = NULL, *cur_ptr = head;

    while(cur_ptr)
    {
      if(cur_ptr->val == val)
      {
        if(NULL == pre_ptr)
        {
          head = head->next;
          delete cur_ptr;
          cur_ptr = head;
        }
        else
        {
          pre_ptr->next = cur_ptr->next;
          delete cur_ptr;
          cur_ptr = pre_ptr->next;
        }
      }
      else
      {
        pre_ptr = cur_ptr;
        cur_ptr = cur_ptr->next;
      }
    }

    return head;
  }
};