2.
public class Main
{
    int num = 5;
    writeNums(num);
}
public static void writeNums(int num)
{
    int num2 = 1;
    writeNums(num, num2);
}
public static void writeNums(int num, int num2)
{
    if(num == num2)
    {
        System.out.println(num);
    }
    else
    {
        System.out.print(num2 + ", ");
        writeNums(num2 + 1);
    }
}
4.
public static int mystery(int n) {
    if (n < 10) {
        return (10 * n) + n;
    } else {
        int a = mystery(n / 10);
        int b = mystery(n % 10);
        return (100 * a) + b;
    }
}
6.
import java.util.*;
public class writeSquares
{
        public static writeSquares(int n)
        {
    int t=n;
    if(n<=0)
        return;
    if(n%2==1)
    {

        System.out.println(n*n);
        writeSquares(--n);

    }
    else
    {

        writeSquares(--n);
        System.out.println(t*t);

    }

}
}
8.
import java.util.*;
import java.io.*;
public class exercises
{
    public static void main(String [] args)
    {
        Scanner console = new Scanner(System.in);
        int n = console.nextInt();
        System.out.println(multiplyEvens(n));


    }
    private static int multiplyEvens(int n) {
        if (n < 1) throw new IllegalArgumentException("Value less than 1 not supported");
        else if (n == 1) return 2;
        else return multiplyEvens(n - 1) * (n * 2);
    }
}
10.
package suarez.com;

import java.util.*;
public class digitMatch
{
    public static void main(String [] args)
    {
        Scanner console = new Scanner(System.in);
        System.out.println("gimme an integer sunny boi(non-negative integer)");
        int x = console.nextInt();
        System.out.println("gimme another integer sunny boi(non-negative integer");
        int y = console.nextInt();
        int count = 0;
        int z = DigitMatch(x, y, count);
        System.out.println("You have" + z + "Digits Matching between your two inputs(");
    }
    public int DigitMatch(int x, int y)
    {
        return DigitMatch( x,y, 0);
    }
    private static int DigitMatch(int x, int y, int count)
    {
        if(x < 0 || y < 0)
        {
            throw new IllegalArgumentException("THATS A FREAKIN NEGATIVE NUMBER");
        }
        if(x == 0 || y == 0)
        {
            return count;
        }
        else
        {
            if(x % 10 == y % 10)
            {
                count++;
            }
            return DigitMatch(x/10, y/10, count);
        }
    }
}
12.
public static boolean isReverse(String word1, String word2) {
    if (word1 == null || word2 == null) {
        return false;
    }
    if (word1.length() == 1 && word2.length() == 1) {
        //Used equals just for fast compare
        return word1.equals(word2);
    } else if (word1.length() == word2.length()) {
        if (word1.charAt(0) == word2.charAt(word2.length() - 1)) {
            String firstWord = word1.substring(1, word1.length());
            String secondWord = word2.substring(0, word2.length() - 1);
            System.out.printf("Trimmed %s, %s to %s, %s\n", word1, word2, firstWord, secondWord);
            return isReverse(firstWord, secondWord);
        } else {
            //Characters didn't matched
            return false;
        }
    } else {
        //Lenght doesn't match
        return false;
    }
}
14.
public static int evenDigits(int n) {
    int rev = 0;
    int digitCount = 0;

    // handle negative arguments
    if (n < 0) return -evenDigits(-n);

    // Extract the even digits to variable rev
    while (n != 0) {
        if (n % 2 == 0) {
            rev = rev * 10 + n % 10;
            digitCount += 1;
        }
        n /= 10;
    }

    // The digits were extracted in reverse order; reverse them again
    while (digitCount > 0) {
        n = n * 10 + rev % 10;
        rev /= 10;
        digitCount -= 1;
    }

    // The result is in n
    return n;
}
16.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SierpinskiCarpet extends JPanel implements ActionListener {


    public static void main(String[] args) {
        JFrame window = new JFrame("Sierpinski Carpet");
        window.setContentPane( new SierpinskiCarpet() );
        window.pack();
        window.setResizable(false);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Dimension screensize = Toolkit.getDefaultToolkit().getScreenSize();
        int x = Math.max(10, (screensize.width - window.getWidth()) / 2);
        int y = Math.max(10, (screensize.height - window.getHeight()) / 2);
        window.setLocation(x,y);
        window.setVisible(true);
    }


    private int level;

    private JRadioButton[] levelButton;

    private JCheckBox[][] regionCheckbox;

    private Display display;


    private class Display extends JPanel {
        Display() {
            setBackground(Color.WHITE);
            setPreferredSize(new Dimension(729,729));
        }
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            drawCarpet(g,level,0,0,729);
        }
    }


    public SierpinskiCarpet() {
        setLayout(new BorderLayout(3,3));
        setBackground(Color.GRAY);
        setBorder(BorderFactory.createLineBorder(Color.GRAY,3));
        display = new Display();
        add(display,BorderLayout.CENTER);
        Box controls = Box.createVerticalBox();
        controls.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        controls.setBackground(Color.WHITE);
        controls.setOpaque(true);
        add(controls, BorderLayout.EAST);
        controls.add(new JLabel("Controls"));
        controls.add(Box.createVerticalStrut(30));
        levelButton = new JRadioButton[7];
        ButtonGroup grp = new ButtonGroup();
        for (int i = 0; i < 7; i++) {
            levelButton[i] = new JRadioButton("Recursion Level " + i);
            grp.add(levelButton[i]);
            levelButton[i].addActionListener(this);
            controls.add(levelButton[i]);
        }
        level = 4;
        levelButton[4].setSelected(true);
        regionCheckbox = new JCheckBox[3][3];
        JPanel checks = new JPanel();
        checks.setLayout(new GridLayout(3,3,5,5));
        for (int r = 0; r < 3; r++) {
            for (int c = 0; c < 3; c++) {
                regionCheckbox[r][c] = new JCheckBox();
                checks.add(regionCheckbox[r][c]);
                regionCheckbox[r][c].addActionListener(this);
                regionCheckbox[r][c].setSelected(true);
            }
        }
        checks.setMaximumSize(new Dimension(90,90));
        checks.setAlignmentX(LEFT_ALIGNMENT);
        checks.setBackground(Color.WHITE);
        regionCheckbox[1][1].setSelected(false);
        controls.add(Box.createVerticalStrut(30));
        controls.add(new JLabel("Regions To Include:"));
        controls.add(Box.createVerticalStrut(15));
        controls.add(checks);
    }



    private void drawCarpet(Graphics g, int level, int x, int y, int size) {
        g.fillRect(x,y,size,size);
    }

}