Question

Write a program that creates a linked list object of 10 characters, then creates a second list object containing a copy of the first list, but in reverse order.

Short answer

Define Node and LinkedList classes, then insert, copy, and reverse characters using methods in the LinkedList class.

Step-by-step solution

Define Node Class

First, we define a class `Node` to represent each node in the linked list. This class will have two attributes: `data` to store the character, and `next` to store a reference to the next node in the list.

Create LinkedList Class

Next, we create a class `LinkedList` that will manage the linked list operations. This class will have a head pointer that refers to the first node in the list.

Implement Insert Method

In the `LinkedList` class, we implement an `insert` method to add a new node at the end of the list. This involves creating a new node and adjusting the pointers such that the last node points to the new node.

Create Method to Print List

To visualize our list, we add a `print_list` method to the `LinkedList` class. This method traverses the list from the head to the end, printing each node's data.

Implement Copy and Reverse

We implement a method `copy_and_reverse` in the `LinkedList` class. This method creates a new `LinkedList` object and inserts nodes in reverse order of traversal of the original list using the concept of inserting nodes at the beginning.

Create First List

Create an instance of `LinkedList` and insert 10 characters into this list to represent the initial sequence.

Copy and Reverse the List

Use the `copy_and_reverse` method on the initial list to generate a new linked list that contains the characters in reverse order.

Output Both Lists

Finally, use the `print_list` method to output both lists – the original list and the reversed copy – to ensure that the method works as expected.

Key concepts

Node Class

At the heart of any linked list is the `Node` class. A node is essentially a data holder. The primary purpose of the `Node` class is to contain and organize information. In our context, each node will store a character. To ensure that nodes are linked, each node also has a reference called `next`. This reference points to the next node in the sequence.
When we traverse a linked list, we move from one node to another using these `next` references. Think of each node as a train car, where each car not only contains passengers (the data) but is also hooked to the next car on the track. If a node's `next` reference is `null` (or `None` in Python), it signifies that this is the end of the list. This setup is crucial for navigating and manipulating linked lists effectively.

Insert Method

To build our linked list, we use the `insert` method. This method is responsible for adding new data (nodes) to the end of the list each time it is called. This is how our train of nodes grows. The `insert` method works by creating a new node with your given data.
If the list is empty, the new node becomes the first node, or the 'head'. If the list already contains some nodes, the method will traverse the list to find the last node. Once it arrives there, the `next` reference of the last node is adjusted to point to this newly created node. This connects the train cars or nodes one after another.
This management of `next` pointers is what builds and maintains the structure of the linked list efficiently.

Print List Method

Visualizing or checking the contents of your linked list is made possible through the `print_list` method. When you call this method, it starts at the head node and traverses each node, printing out the data it holds.
This method is essentially looping through each 'train car' in our list, stopping at each one to read and display the contents. It continues this process until it reaches a node where the `next` is `null`, indicating it's the last node.
Using `print_list` helps in debugging and confirming that our linked list structure is correctly formed and ordered. It's a simple but effective way to ensure all nodes are connected as expected.

Copy and Reverse Method

The `copy_and_reverse` method is a creative way to manipulate the linked list. This method takes an existing list and creates a new one, but in reverse order. Imagine having a train where you want to reverse the arrangement of all cars without just turning the train around.
To implement this, the method traverses the original list, using each node's data to create nodes in a new list. However, instead of adding these nodes to the end as before, each new node is inserted at the beginning of the new list. The result is a list that appears to be a mirror image of the original one.
This technique cleverly uses node insertion at the head to build the reversed list. It's an efficient and effective way to create a reversed copy without altering the original list.