Collections and Data Structures – Data Structures (linked lists, trees, graphs)

Introduction

Data structures are fundamental components in computer science and software development. In Java, you have access to a variety of data structures that allow you to efficiently organize and manipulate data. In this guide, we’ll explore some of the most commonly used data structures, including linked lists, trees, and graphs, and how they can be implemented in Java.

Linked Lists

A linked list is a data structure that consists of a sequence of elements, where each element is connected to the next one through a link or reference. Linked lists come in various forms, such as singly linked lists, doubly linked lists, and circular linked lists. They are flexible and dynamic, making them suitable for use cases like implementing stacks and queues.

Example:

Here’s an example of a singly linked list in Java:

class Node {
    int data;
    Node next;

    Node(int data) {
        this.data = data;
        next = null;
    }
}

public class SinglyLinkedList {
    Node head;

    // Methods to manipulate the linked list
}

Trees

Trees are hierarchical data structures that consist of nodes connected by edges. They have a root node at the top and branching structures that lead to child nodes. Common types of trees include binary trees, binary search trees, and balanced trees like AVL and Red-Black trees. Trees are used for various purposes, such as searching and sorting.

Example:

Here’s an example of a binary search tree in Java:

class Node {
    int data;
    Node left, right;

    Node(int data) {
        this.data = data;
        left = right = null;
    }
}

public class BinarySearchTree {
    Node root;

    // Methods to manipulate the binary search tree
}

Graphs

Graphs are versatile data structures consisting of nodes (vertices) and edges connecting these nodes. They can represent complex relationships and are used in various applications, including network design, social network analysis, and pathfinding algorithms. Graphs can be directed (edges have a direction) or undirected (edges have no direction).

Example:

Here’s an example of representing a graph using an adjacency list in Java:

import java.util.*;

public class Graph {
    private int vertices;
    private List<List<Integer>> adjacencyList;

    public Graph(int vertices) {
        this.vertices = vertices;
        adjacencyList = new ArrayList<>(vertices);

        for (int i = 0; i < vertices; i++) {
            adjacencyList.add(new ArrayList<>());
        }
    }

    // Methods to manipulate the graph
}

Choosing the Right Data Structure

Selecting the appropriate data structure is essential for solving specific problems efficiently. Linked lists are great for dynamic lists, trees are suitable for hierarchical data, and graphs are perfect for modeling relationships. When working with data, understanding these data structures can significantly enhance your problem-solving capabilities in Java.

Conclusion

Data structures are the backbone of computer science and programming. In Java, you have a wide range of data structures at your disposal, each with its unique properties and use cases. By mastering these structures, you can optimize your code and tackle complex problems effectively.