How to create a circular linked list with helper methods in C++

Key takeaways:

• A circular linked list differs from other lists in that the last node points back to the head, creating a loop. This structure allows continuous traversal from any point in the list.

• Each node in a circular linked list contains data and a pointer to the next node. The list class includes essential pointers (head and optionally tail) for managing the list efficiently.

• Essential operations like adding nodes (to the head or tail), traversing, finding, and removing nodes are straightforward and leverage the circular structure. Each method is designed to maintain the looped nature of the list.

• Adding or removing nodes from the head or tail can often be done in O(1) time, while traversal and finding a node take O(n) time. All operations use constant space, making circular linked lists efficient in memory usage.

• Circular linked lists are well-suited for applications like round-robin scheduling, cyclic buffers, and multiplayer games, where cyclic data processing is beneficial.

• Mastering circular linked lists is a foundation for exploring more advanced data structures like doubly circular linked lists and circular queues, which build on similar principles.

Linked lists are one of the fundamental data structures in computer science. They consist of nodes, each containing data and a pointer to the next node, creating a sequence of elements. Unlike arrays, linked lists do not require a contiguous block of memory, which makes them more flexible for dynamic data storage. They allow efficient insertion and deletion operations, especially when the size of the data set is unknown in advance.

A circular linked list is a special type of linked list where the last node points back to the first node, forming a circular structure. This can be further categorized as follows:

• Singly circular linked list: Each node points to the next node, and the last node points back to the first node.

• Doubly circular linked list: Each node has two pointers, one to the next node and one to the previous node, with the last node's "next" pointer pointing to the head and the head's "previous" pointer pointing to the last node.

This circular structure eliminates the need for a "null" pointer at the end, allowing continuous traversal from any point in the list. It also enables more efficient looping through data, as the list can be navigated back to the start seamlessly.

Setting up the circular linked list in C++

Let's see how we can setup circular linked list in C++:

Node structure

To start, we define the structure of a node that will be used in our circular linked list. Each node will contain:

• A data field to store the node’s value.

• A next pointer to reference the next node in the list.

Here’s the basic structure of a node:

In a circular linked list, the next pointer of the last node will eventually point back to the head node, creating a loop in the list.

Circular linked list class

Next, we define the class for our circular linked list. This class will include:

• A head pointer, which points to the first node in the list. If the list is empty, head will be nullptr.

• A tail pointer (optional, but useful for certain operations), which can point to the last node, allowing efficient insertion at the end.

Here’s the basic structure of the circular linked list class:

Essential helper methods

Here are the essential helper methods for the circular linked list, each implemented to handle the circular nature of the list.

Adding nodes

• addToHead: Inserts a new node at the beginning of the circular linked list.

• addToTail: Inserts a new node at the end of the circular linked list.

Traversing the list

To print all the nodes in the circular linked list, we need to consider the circular nature to avoid infinite looping.

Finding a node

This method searches for a node by its value. If the node is found, it returns a pointer to the node; otherwise, it returns nullptr.

Removing nodes

• removeHead: Removes the head node from the list.

• removeTail: Removes the last node from the list.

• removeByValue: Removes a node by its value. If the node is found, it is removed; if not, the list remains unchanged.

These helper methods provide a full range of functionalities for adding, finding, and removing nodes in the circular linked list while preserving the circular structure. Each method is designed to handle both typical cases and edge cases (like an empty list or a single-node list).

Complete code

This is the complete implementation of the CircularLinkedList class in C++ with all the helper methods discussed earlier. The accompanying main.cpp file includes examples and test cases to demonstrate the functionality of each method, while CircularLinkedList.cpp contains the method definitions for better modularity and readability.

Complexity analysis

Here's a table outlining the time and space complexity for each helper method in the CircularLinkedList class.

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