Implementing A Singly or Doubly Linked List in Java - A LeetCode Question
Introduction
Linked Lists are one of the most important data structures in computer science. They are used to store data and can be manipulated to solve various problems. In this article, we will be looking at a LeetCode question that involves implementing a linked list in Java.
What Is A Linked List?
A linked list is a data structure that consists of a group of nodes which together represent a sequence. Each node contains a data element and a pointer to the next node in the sequence. The last node in the linked list points to null indicating the end of the list. Linked lists can be either singly-linked or doubly-linked.
Singly Linked List
A singly-linked list is a linked list in which each node contains a data element and a pointer to the next node in the sequence. The last node in the list points to null. The advantage of a singly-linked list is that it is easy to implement and is relatively efficient in terms of memory usage.
Doubly Linked List
A doubly-linked list is a linked list in which each node contains a data element and two pointers. The first pointer points to the previous node in the sequence and the second pointer points to the next node in the sequence. The last node in the list points to null. The advantage of a doubly-linked list is that it allows for traversal in both directions.
LeetCode Question
The LeetCode question that we will be looking at involves implementing a singly or doubly linked list in Java. The question states: "Implement a linked list class. The class should have a head, tail, and length property. The class should also have the following methods: isEmpty, addToTail, addToHead, removeTail, removeHead, and search."
Solution
The solution to this problem involves creating a LinkedList class with the specified properties and methods. The LinkedList class should have two fields: a head and a tail. The head and tail will both be references to Node objects. Each Node object should contain a data element and a reference to either the next or previous Node object in the list. The methods can then be implemented as follows:
isEmpty()
The isEmpty() method should check if the head and tail are both null. If they are, then the list is empty and the method should return true. Otherwise, it should return false.
addToTail()
The addToTail() method should add a new Node to the end of the list. To do this, the method should check if the list is empty. If it is, then the new Node should be set as both the head and the tail of the list. Otherwise, the new Node should be set as the tail and the old tail should be updated to point to the new Node.
addToHead()
The addToHead() method should add a new Node to the beginning of the list. To do this, the method should check if the list is empty. If it is, then the new Node should be set as both the head and the tail of the list. Otherwise, the new Node should be set as the head and the old head should be updated to point to the new Node.
removeTail()
The removeTail() method should remove the Node at the end of the list. To do this, the method should check if the list is empty. If it is, then the method should return null. Otherwise, the Node at the end of the list should be removed, and the tail should be updated to point to the new last Node in the list.
removeHead()
The removeHead() method should remove the Node at the beginning of the list. To do this, the method should check if the list is empty. If it is, then the method should return null. Otherwise, the Node at the beginning of the list should be removed, and the head should be updated to point to the new first Node in the list.
search()
The search() method should search the list for a Node containing the specified data element. To do this, the method should start at the head of the list and traverse the list until it either finds a Node containing the specified data element or reaches the end of the list. If it finds a Node containing the specified data element, then it should return the Node. Otherwise, it should return null.