203. Remove Linked List Elements

203. 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

My Solutions:

这一题要返回ListNode，所以必须要有dummy记录开头。

class Solution {
    public ListNode removeElements(ListNode head, int val) {
        
        // because we will move head, must have a dummy to return head
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        // because we will connect the element removed's before and after elements, we must do the operation on the element before it
        head = dummy;
        while(head.next != null) {
            if (head.next.val == val) {
                head.next = head.next.next; // skip the element at head.next
            } else {
                head = head.next;
            }
        }
        return dummy.next;
    }
}