Java Data Structures and Algorithms

This repository contains clean, educational implementations of classic sorting algorithms and fundamental data structures, written in Java as part of my preparation for competitive IT exams and as a technical complement to my project OOPPS.

All classes and methods follow standard English terminology after a full refactor focused on consistency and clarity.

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🎯 Purpose

• Strengthen understanding of classical data structures and algorithms
• Maintain a clean and readable educational codebase
• Support my exam preparation and reinforce Java fundamentals
• Serve as a simple, transparent reference for algorithmic concepts

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🧰 Tech Stack

• Java 17+
• No external dependencies
• Pure Java and standard library only

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🔃 Sorting Algorithms

All sorting implementations include ascending and descending variants, plus small demo main methods.

• BubbleSort
• MergeSort
• QuickSort (Lomuto partition scheme)

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📦 Data Structures

Generic, ready-to-use data structures implemented from scratch:

• Stack (LIFO)
• Queue (FIFO)
• SinglyLinkedList
• DoublyLinkedList

Each structure includes:

• basic operations (push/pop, enqueue/dequeue, etc.)
• size and state checks
• console-based demo methods

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🧪 Examples

Sorting Algorithms

QuickSort example

int[] data = { 5, 1, 4, 2, 8 };

QuickSort.sortAscending(data);

System.out.println(Arrays.toString(data)); // [1, 2, 4, 5, 8]

Run the demo

javac -d out src/com/nespapu/sorting/*.java
java -cp out com.nespapu.sorting.QuickSortDemo

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Data Structures

Doubly Linked List

DoublyLinkedList<Integer> list = new DoublyLinkedList<>();
list.addLast(10);
list.addLast(20);
list.addLast(30);

list.printList();        // [10, 20, 30]
list.printListReverse(); // [30, 20, 10]

Singly Linked List

SinglyLinkedList<Integer> list = new SinglyLinkedList<>();
list.addLast(1);
list.addLast(2);
list.addLast(3);

list.printList(); // [1, 2, 3]

Stack

Stack<String> stack = new Stack<>();
stack.push("A");
stack.push("B");
stack.push("C");

System.out.println(stack.pop());   // C
System.out.println(stack.peek());  // B
System.out.println(stack.isEmpty()); // false

Queue

Queue<Integer> queue = new Queue<>();
queue.enqueue(10);
queue.enqueue(20);
queue.enqueue(30);

System.out.println(queue.dequeue()); // 10
System.out.println(queue.peek());    // 20

Run the demo

javac -d out src/com/nespapu/structures/*.java
java -cp out com.nespapu.structures.QueueDemo

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📌 Next Steps

Planned improvements include:

• Adding unit tests (JUnit)
• Expanding the repository with additional algorithms and data structures

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📄 License

This project is open-source and distributed under the MIT License.
Copyright © 2025–present Néstor Pavón Puro.
For more information, see the LICENSE file.

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