Singly Linked List

A typescript implementation of a singly linked list data structure.

Description

In simple terms, a singly linked list is a data structure that consists of one or more 'nodes'. Each node has a data field (which can contain any data--a primitive value or complex object) and a pointer to the next 'node'. This differs from a 'doubly linked list' in that it does NOT contain a reference, or link, to the previous node. The implication of this means one can only traverse the list in one direction, starting from the head node. The idea of having a link to the next node is where this data structure gets its descriptive name.

This implementation provides basic functionality of adding nodes to the front or back of the list, as well as the ability to insert a node at a given position in the list. It also provides the ability to remove nodes at the front or back of the list, or from any given position.

The find, or search, functionality provides the ability to find the first node containing specified data. It also provides the ability to find a node given a specific position, or index, in the list.

For specific examples and documentation, see the below sections

Motivation:

The main purpose of this project is revisit the basics, and focus on the development process.

I wholehearedly acknowledge that the basic data structure space is populated with well-written code and efficient implementations, and one could easily grab one of those libraries and integrate it in their project. However, the main difference between those libraries/implementations and this one is that this is the best implementation I have ever written. My hope is that someone else will find this useful, but understand, this code is not the goal; this will simply be a useful bi-product of the journey. The underlying motivation is to understand and, more importantly, learn from the process to get to the desired end-state—for me it is all about the joy of the journey.

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Basic Usage

Install with npm :

npm install singly-linked-list --save

Basic usage example below. Note: it does not cover all the available methods, rather just highlights the main functionality to get up and running with this data structure. For a description of all the methods, see the API section.

var LinkedList = require('singly-linked-list');
var list = new LinkedList();

list.isEmpty();
// --> true

list.insert('data item 1');
list.insert('data item 2');
list.insert('data item 3');
list.insert('data item 4');
// list contains:
// 'data item 1', ... ,'data item 4'

// alternatively, the list can be initialized with an array
var initialData = ['data item 1', 'data item 2', 'data item 3', 'data item 4'];
var populatedList = new LinkedList(initialData);
// populatedList contains:
// 'data item 1', ... ,'data item 4'

list.isEmpty();
// --> false

list.getSize();
// --> 4

list.insertFirst('data item 0');
// list contains:
// 'data item 0', ... ,'data item 4'

list.getHeadNode().getData();
// --> 'data item 0'

list.remove();
// --> removes 'data item 4'

list.removeFirst();
// --> removes 'data item 0'

list.getHeadNode().getData();
// --> 'data item 1'

list.clear();
list.isEmpty();
// --> true

API

Available methods for a singly-linked-list instance:

• getHeadNode()

  Returns the first node in the list

• getTailNode()

  Returns the last node in the list

• isEmpty()

  Determines if the list is empty or not. Returns true if is empty, false otherwise.

• getSize()

  Returns the size of the list, or number of nodes

• clear()

  Clears the list of all nodes/data

• insert(data)

  Inserts a node (with the provided data) to the end of the list

• insertFirst(data)

  Inserts a node (with the provided data) to the front of the list

• insertAt(index, data)

  Inserts a node (with the provided data) at the index indicated.

• insertBefore(nodeData, dataToInsert)

  Inserts a node (with the dataToInsert) before the first node containing nodeData

• insertAfter(nodeData, dataToInsert)

  Inserts a node (with the dataToInsert) after the first node containing nodeData

• remove()

  Removes the tail node from the list

• removeFirst()

  Removes the head node from the list

• removeAt(index)

  Removes the node at the index provided

• removeNode(nodeData)

  Removes the first node that contains the nodeData provided

• indexOf(nodeData)

  Returns the index of the first node containing the provided nodeData. If a node cannot be found containing the provided data, null is returned.

• contains(nodeData)

  Determines whether or not the list contains the provided nodeData

• find(nodeData)

  Returns the fist node containing the provided nodeData. If a node cannot be found containing the provided data, null is returned.

• findAt(index)

  Returns the node at the location provided by index

• forEach(fn)

  Utility function to iterate over the list and call the fn provided on each node, or element, of the list

• toArray()

  Returns an array of all the data contained in the list

• printList()

  Prints to the console the data property of each node in the list

Available methods for an individual node instance:

• getData()

  Returns the data of the the node

• hasNext()

  Returns whether or not the node has a pointer to the next node

• toString()

  Returns a string represenation of the node. If the data is an object, it returns the JSON.stringify version of the object. Otherwise, it simply returns the data

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License

MIT © Jason Jones