2.1

# remove duplicates from an unsorted linked list.

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    def removeDuplicates(self):
        current = self.head
        element_list = set()
        prev = None
        while (current is not None):
            if current.data not in element_list:
                element_list.add(current.data)
                prev = current
                current = current.next
            else:
                prev.next = current.next
                current = current.next


    def printList(self):
        current = self.head
        while current:
            print(current.data)
            current = current.next

l = LinkedList()
l.push(15)
l.push(14)
l.push(16)
l.push(15)
l.push(16)
l.printList()
print("===============")
l.removeDuplicates()
l.printList()