83. Remove Duplicates from Sorte

思路：复制链表的head指针，依次比较当前指针的值和下一个是否相等

public ListNode deleteDuplicates(ListNode head) {
        ListNode current = head;
        while (current != null && current.next != null) {
            if (current.val == current.next.val) {
                current.next = current.next.next;
            } else {
                current = current.next;
            }
        }
        return head;
    }