1. Thinking Recursively

Exercise 1: Write a recursive function in Java to compute the nth Fibonacci number.

Reveal Answer

public class Fibonacci {
    public static int fibonacci(int n) {
        if (n <= 1) {
            return n;
        }
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
    
    public static void main(String[] args) {
        System.out.println(fibonacci(10)); // Example test
    }
}
    

Exercise 2: Implement a recursive function to calculate the factorial of a number.

Reveal Answer

public class Factorial {
    public static int factorial(int n) {
        if (n == 0) return 1;
        return n * factorial(n - 1);
    }
}
    

2. Abstract Data Structures

Exercise 1: Implement a stack using an array in Java, supporting push, pop, and peek operations.

Reveal Answer

class Stack {
    private int[] stack;
    private int top;
    
    public Stack(int size) {
        stack = new int[size];
        top = -1;
    }
    
    public void push(int value) {
        if (top == stack.length - 1) {
            System.out.println("Stack Overflow");
            return;
        }
        stack[++top] = value;
    }
    
    public int pop() {
        if (top == -1) {
            System.out.println("Stack Underflow");
            return -1;
        }
        return stack[top--];
    }
}
    

3. Linked Lists

Exercise: Implement a singly linked list in Java with methods to add and remove nodes.

Reveal Answer

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

class LinkedList {
    private Node head;
    
    public void add(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
            return;
        }
        Node temp = head;
        while (temp.next != null) {
            temp = temp.next;
        }
        temp.next = newNode;
    }
}
    

4. Trees

Exercise: Implement a basic binary search tree (BST) with insertion and in-order traversal.

Reveal Answer

class TreeNode {
    int value;
    TreeNode left, right;
    
    public TreeNode(int value) {
        this.value = value;
        left = right = null;
    }
}

class BinarySearchTree {
    private TreeNode root;
    
    public void insert(int value) {
        root = insertRec(root, value);
    }
    
    private TreeNode insertRec(TreeNode root, int value) {
        if (root == null) {
            return new TreeNode(value);
        }
        if (value < root.value) {
            root.left = insertRec(root.left, value);
        } else {
            root.right = insertRec(root.right, value);
        }
        return root;
    }
}
    

Keep Practicing!

By practicing these exercises, you will build a solid foundation in key computer science concepts. Try modifying the code, adding additional functionalities, or implementing alternative approaches to reinforce your learning!