JavaExam.md
---
### 1. Abstract Data Types (ADTs)

#### Easy

Which ADT uses a Last-In-First-Out (LIFO) policy?

* Array
* Stack
* Queue
* LinkedList
---

Describe a real-life scenario where a stack data structure could be used effectively. How would push, pop, and peek operations correspond to actions in this scenario?

---

Explain how a queue data structure might be used in the management of print jobs on a printer. How would the enqueue, dequeue, and peek operations be utilized?

---

What are some advantages and disadvantages of using a LinkedList over an Array in certain scenarios? Give an example of a scenario where a LinkedList would be a better choice.

#### Hard

Implement a basic queue using only a stack data structure. The queue should support `enqueue`, `dequeue`, and `peek` operations.

import java.util.Stack;

public class QueueUsingStacks {

    //ADD STUFF HERE

    public void enqueue(int x) {
       //TODO
    }

    public int dequeue() {
        //TODO

    }
    public int peek() {
        //TODO
    }

}

### 2. Binary Trees

#### Easy

In a Binary Search Tree, if all nodes to the right contain larger values, then all nodes to the left of the parent node contain...:

A. Smaller values

B. Larger values

C. Equal values

D. Random values

---

What is the maximum height for a binary tree that has `n` nodes.

#### Hard Question:

---
What is the minimum height for a binary tree that has `n` nodes.

---

Write a recursive function that checks whether a binary tree is a valid binary search tree.


---

What is the worst-case time complexity of searching for a value in a binary search tree?

A. O(log n)

B. O(n)

C. O(1)

D. O(n log n)

### 3. Recursion/Iteration

#### Easy Question:

How many base cases can you have for a recursive function?

A. Exactly 1

B. Infinite

C. Any finite number greater than 0

D. 0 or 1

---

Write both an iterative and recursive function to compute the factorial of a given non-negative integer.

---

Write both an iterative and recursive function `power2` where `power2(n) = 2 ^ n` that is `2 * 2 * 2 ...` `n` times.

---

Which of the following problems can be solved using recursion?

A. Computing factorials

B. Traversing a tree

C. Performing a binary search

D. All of the above

### Hard:

This is an inorder traversal

class BinaryTree {
    Node root;

    void inorderTraversal(Node node) {
        if (node == null) {
            return;
        }

        /* first recur on left child */
        inorderTraversal(node.left);

        /* then print the data of node */
        System.out.print(node.value + " ");

        /* now recur on right child */
        inorderTraversal(node.right);
    }

    // Wrapping function
    void inorderTraversal() {
        inorderTraversal(root);
    }
}

Rewrite it using an iterative method.

---

Write a java method that takes a string that can contain three types of brackets, which are `(), [], {}`.
It should return whether they are matching. For instance, `((()))` and `({[][]})` are matching, but `())`, `([(])`, `)(` and `({)}` are not.

---
In general, how do you transform recursive method into an iterative one?

### 4. Stream (lambda expression)

#### Easy

Write a method using Java 8 Streams that calculates the product of all numbers in a list.

---
Implement a method using Java 8 Streams to count the number of strings in a list that have more than 5 characters.

---

Implement a method using Java 8 Streams that takes a list of integers and returns a new list containing only the even numbers.

---

What does the `map` operation do on a Stream in Java 8?

A. Filters elements based on a condition

B. Transforms the elements of the stream

C. Reduces the elements to a single summary element

D. Limits the number of elements in the stream

---

Consider the following Java code snippet:

List<String> names = Arrays.asList("John", "Jane", "Jill", "James");
names.stream().filter(name -> name.startsWith("J")).count();

What will be the output of the above code?

A. 4

B. 3

C. 2

D. 1

---

What does this code do ?

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("Apple", "Banana", "Cherry", "Blueberry", "Elderberry");

        List<String> sortedWords = words.stream()
                .sorted(Comparator.comparing(String::length))
                .collect(Collectors.toList());

        System.out.println(sortedWords);  
    }
}

#### Hard

Implement a method using Java 8 Streams that takes a list of numbers and returns the list sorted in ascending order, but without any duplicate numbers.

---

Look at this code.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {

    public static class Fruit implements Comparable<Fruit> {
        private String name;

        public Fruit(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }

        @Override
        public int compareTo(Fruit otherFruit) {
            // Reverse order by name
            return __________  // REPLACE HERE
        }

        @Override
        public String toString() {
            return this.name;
        }
    }

    public static void main(String[] args) {
        List<Fruit> fruits = Arrays.asList(
                new Fruit("Apple"),
                new Fruit("Banana"),
                new Fruit("Cherry"),
                new Fruit("Blueberry"),
                new Fruit("Elderberry"));

        List<Fruit> sortedFruits = fruits.stream()
                .sorted()
                .collect(Collectors.toList());

        System.out.println(sortedFruits);   
    }
}

How do you change the `compareTo` method so the output is `[Elderberry, Cherry, Blueberry, Banana, Apple]`

### 5. Hashing (HashMap)

#### Easy Question:

In a HashMap, data is stored using:

A. Key-Value pairs

B. Queues

C. Stacks

D. Arrays

#### Hard Question

Given a string S, use hash maps to make a function `f` return all characters in the string that occur at least 5 times. For example `f("aaaaaaaaaaaabaaaaaaacaaaaadeeeffffffff")` will return `"af"`. It doesn't matter if you return `"af"` or `"fa"`. Implement `f`.

### XML

#### Easy Question

What does XML stand for?

A. eXtensible Markup Language

B. eXtensible Madeup Language

C. eXample Machine Learning

D. Xenophobic Mario Luigi

---

Which of the following is a self-closing tag in XML?

A. `<tag> </tag>`

B. `<tag>`

C. `<tag/>`

D. `</tag>`

# Conclusion

Blame errors on ChatGPT.

JavaExam.md
---
### 1. Abstract Data Types (ADTs)

#### Easy

Which ADT uses a Last-In-First-Out (LIFO) policy?

* Array
* Stack
* Queue
* LinkedList
---

Describe a real-life scenario where a stack data structure could be used effectively. How would push, pop, and peek operations correspond to actions in this scenario?

---

Explain how a queue data structure might be used in the management of print jobs on a printer. How would the enqueue, dequeue, and peek operations be utilized?

---

What are some advantages and disadvantages of using a LinkedList over an Array in certain scenarios? Give an example of a scenario where a LinkedList would be a better choice.

#### Hard

Implement a basic queue using only a stack data structure. The queue should support `enqueue`, `dequeue`, and `peek` operations.

import java.util.Stack;

public class QueueUsingStacks {

    //ADD STUFF HERE

    public void enqueue(int x) {
       //TODO
    }

    public int dequeue() {
        //TODO

    }
    public int peek() {
        //TODO
    }

}

### 2. Binary Trees

#### Easy

In a Binary Search Tree, if all nodes to the right contain larger values, then all nodes to the left of the parent node contain...:

A. Smaller values

B. Larger values

C. Equal values

D. Random values

---

What is the __maximum__ height for a binary tree that has `n` nodes.

#### Hard Question:

---
What is the __minimum__ height for a binary tree that has `n` nodes.

---

Write a recursive function that checks whether a binary tree is a valid binary search tree.


---

What is the worst-case time complexity of searching for a value in a binary search tree?

A. O(log n)

B. O(n)

C. O(1)

D. O(n log n)

### 3. Recursion/Iteration

#### Easy Question:

How many base cases can you have for a recursive function?

A. Exactly 1

B. Infinite

C. Any finite number greater than 0

D. 0 or 1

---

Write both an iterative and recursive function to compute the factorial of a given non-negative integer.

---

Write both an iterative and recursive function `power2` where `power2(n) = 2 ^ n` that is `2 * 2 * 2 ...` `n` times.

---

Which of the following problems can be solved using recursion?

A. Computing factorials

B. Traversing a tree

C. Performing a binary search

D. All of the above

### Hard:

This is an inorder traversal

class BinaryTree {
    Node root;

    void inorderTraversal(Node node) {
        if (node == null) {
            return;
        }

        /* first recur on left child */
        inorderTraversal(node.left);

        /* then print the data of node */
        System.out.print(node.value + " ");

        /* now recur on right child */
        inorderTraversal(node.right);
    }

    // Wrapping function
    void inorderTraversal() {
        inorderTraversal(root);
    }
}

Rewrite it using an iterative method.

---

Write a java method that takes a string that can contain three types of brackets, which are `(), [], {}`.
It should return whether they are matching. For instance, `((()))`, `()(){}[]` and `({[][]})` are matching, but `())`, `([(])`, `)(` and `({)}` are not.

---
In general, how do you transform recursive method into an iterative one?

### 4. Stream (lambda expression)

#### Easy

Write a method using Java 8 Streams that calculates the product of all numbers in a list.

---
Implement a method using Java 8 Streams to count the number of strings in a list that have more than 5 characters.

---

Implement a method using Java 8 Streams that takes a list of integers and returns a new list containing only the even numbers.

---

What does the `map` operation do on a Stream in Java 8?

A. Filters elements based on a condition

B. Transforms the elements of the stream

C. Reduces the elements to a single summary element

D. Limits the number of elements in the stream

---

Consider the following Java code snippet:

List<String> names = Arrays.asList("John", "Jane", "Jill", "James");
names.stream().filter(name -> name.startsWith("J")).count();

What will be the output of the above code?

A. 4

B. 3

C. 2

D. 1

---

What does this code do ?

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("Apple", "Banana", "Cherry", "Blueberry", "Elderberry");

        List<String> sortedWords = words.stream()
                .sorted(Comparator.comparing(String::length))
                .collect(Collectors.toList());

        System.out.println(sortedWords);  
    }
}

#### Hard

Implement a method using Java 8 Streams that takes a list of numbers and returns the list sorted in ascending order, but without any duplicate numbers.

---

Look at this code.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {

    public static class Fruit implements Comparable<Fruit> {
        private String name;

        public Fruit(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }

        @Override
        public int compareTo(Fruit otherFruit) {
            // Reverse order by name
            return __________  // REPLACE HERE
        }

        @Override
        public String toString() {
            return this.name;
        }
    }

    public static void main(String[] args) {
        List<Fruit> fruits = Arrays.asList(
                new Fruit("Apple"),
                new Fruit("Banana"),
                new Fruit("Cherry"),
                new Fruit("Blueberry"),
                new Fruit("Elderberry"));

        List<Fruit> sortedFruits = fruits.stream()
                .sorted()
                .collect(Collectors.toList());

        System.out.println(sortedFruits);   
    }
}

How do you change the `compareTo` method so the output is `[Elderberry, Cherry, Blueberry, Banana, Apple]`

### 5. Hashing (HashMap)

#### Easy Question:

In a HashMap, data is stored using:

A. Key-Value pairs

B. Queues

C. Stacks

D. Arrays

#### Hard Question

Given a string S, use hash maps to make a function `f` return all characters in the string that occur at least 5 times. For example `f("aaaaaaaaaaaabaaaaaaacaaaaadeeeffffffff")` will return `"af"`. It doesn't matter if you return `"af"` or `"fa"`. Implement `f`.

### XML

#### Easy Question

What does XML stand for?

A. eXtensible Markup Language

B. eXtensible Madeup Language

C. eXample Machine Learning

D. Xenophobic Mario Luigi

---

Which of the following is a self-closing tag in XML?

A. `<tag> </tag>`

B. `<tag>`

C. `<tag/>`

D. `</tag>`

# Conclusion

Blame errors on ChatGPT.