Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

public class Solution {
    //Time: O(n)  Space: O(1)
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        
        ListNode node = head;
        while (node.next != null) {
            if (node.next.val == node.val) {
                node.next = node.next.next;
            } else {
                node = node.next;
            }
        }
        return head;
    }
}