#### Overview of this book

Java 9 Data Structures and Algorithms covers classical, functional, and reactive data structures, giving you the ability to understand computational complexity, solve problems, and write efficient code. This book is based on the Zero Bug Bounce milestone of Java 9. We start off with the basics of algorithms and data structures, helping you understand the fundamentals and measure complexity. From here, we introduce you to concepts such as arrays, linked lists, as well as abstract data types such as stacks and queues. Next, we’ll take you through the basics of functional programming while making sure you get used to thinking recursively. We provide plenty of examples along the way to help you understand each concept. You will also get a clear picture of reactive programming, binary searches, sorting, search trees, undirected graphs, and a whole lot more!
Java 9 Data Structures and Algorithms
Credits
www.PacktPub.com
Customer Feedback
Preface
Free Chapter
Why Bother? – Basic
Cogs and Pulleys – Building Blocks
Protocols – Abstract Data Types
Detour – Functional Programming
Efficient Searching – Binary Search and Sorting
Efficient Sorting – quicksort and mergesort
Concepts of Tree
More About Search – Search Trees and Hash Tables
Concepts of Graph
Reactive Programming
Index

## Double ended queue

A double ended queue is a combination of a stack and a queue. The idea is that you are allowed to insert and remove elements at both ends of the queue. If you remove elements from the side you have inserted, it will behave like a stack. On the other hand, if you insert and remove on opposite ends, it will behave like a queue. You can mix these operations and use them in any order you like. The following figure shows a few operations to clarify this idea:

A double ended queue has the following operations all with a complexity of O(n):

• Push: This inserts an element at the beginning

• Pop: This removes an element from the beginning

• Inject: This inserts an element at the end

• Eject: This removes an element from the end

• Peek: This checks the first element

• PeekLast: This checks the last element

A double ended queue will be represented by the following interface:

```public interface DoubleEndedQueue<E> extends Stack<E> {
void inject(E value);
E eject();
E peekLast(...```