from typing import Optional
from utils import ListNode, list_to_linklist

def deleteDuplicates(head: Optional[ListNode]) -> Optional[ListNode]:
    if not head:
        return head

    p = head
    while p.next:
        if p.val == p.next.val:
            p.next = p.next.next
        else:
            p = p.next

    return head

print(deleteDuplicates(list_to_linklist([1, 1, 2])))