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


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

    def append(self, data):
        new = Node(data)
        if self.head is None:
            self.head = new
            return
        last = self.head
        while (last.next):
            last = last.next
        last.next = new

    def print(self):
        val = self.head
        while val is not None:
            if val.next is None:
                print(val.data)
            else:
                print(val.data, end=" -> ")
            val = val.next

    def length(self):
        temp = self.head
        count = 0
        while (temp != None):
            count += 1
            temp = temp.next
        return count

    def insert(self, data, index):
        new = Node(data)
        if (index == 0):
            new.next = self.head
            self.head = new
        else:
            temp = self.head
            for i in range(1, index):
                if (temp != None):
                    temp = temp.next
            if (temp != None):
                new.next = temp.next
                temp.next = new
            else:
                print("\nThe previous node is null.")

    def index(self, data):
        temp = self.head
        index = 0
        while (temp != None):
            if (temp.data == data):
                return index
            temp = temp.next
            index += 1
        return -1

    def delete(self, index):
        if (index == 0):
            self.head = self.head.next
        elif (index >= self.length()):
            return
        else:
            temp = self.head
            for i in range(1, index):
                if (temp != None):
                    temp = temp.next
            if (temp != None):
                temp.next = temp.next.next
            else:
                print("\nThe previous node is null.")


if __name__ == "__main__":
    L = LinkedList()
    L.append(2)
    L.append(3)
    L.append(1)
    L.append(4)
    L.print()           # 1 -> 3
    L.insert(4, 3)
    L.insert(1, 0)
    L.insert(3, 2)
    L.insert(2, 1)
    L.print()           # 15 -> 1 -> 10 -> 3
    print(L.index(1))   # 1
    L.delete(0)
    L.delete(1)
    L.delete(4)
    L.delete(5)
    L.print()           # 1 -> 10 -> 3