如何通过保留顺序来删除链表中的重复项

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def deleteDuplicates(head):
    if not head:
        return head
    
    current = head
    while current.next:
        if current.val == current.next.val:
            current.next = current.next.next
        else:
            current = current.next
    
    return head