LC.203. Remove Linked List Elements

230,82,83 是一类题 

https://leetcode.com/problems/remove-linked-list-elements/description/
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

  time o(1) space o(1)

 public ListNode removeElements(ListNode head, int val) {
        //这里不要写 HEAD.NEXT == NULL 返回 HEAD, 因为会出现 [1], VAL=1 -> []
        if (head == null ) return head;
        ListNode dummy = new ListNode(0) ;
        ListNode curr = dummy ;
        dummy.next = head ;
        /*
        Given: 1 --> 2 --> 6 --> 6 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6
        Return: 1 --> 2 --> 3 --> 4 --> 5
        * */
        while (curr != null && curr.next!= null){
            if (curr.next.val == val){
                curr.next = curr.next.next ;
            } else{
                curr = curr.next ;
            }
        }
        return dummy.next ;
    }