# Linked List

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


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

    def indexOf(self, key) -> int:
        current = self.head
        index = 0
        while current is not None:
            if current.key == key:
                return index
            index += 1
            current = current.next
        return -1

    def add_list_item(self, item: Node) -> None:
        if not self.head:
            self.head = item
        else:
            self.tail.next = item
        self.tail = item


list1 = LinkedList()

print(list1.indexOf("b"))
# >>> print(list1.indexOf("b"))
# -1

list1.add_list_item(Node("a", "b"))
list1.add_list_item(Node("b", "c"))

print(list1.indexOf("b"))
# >>> print(list1.indexOf("b"))
# 1