RecursionExercises.java

import java.util.Scanner;
//*******************************************************
// RecursionExercises.java
// the class reprsents RecursionExercises
// Author: liron mizrahi
//*******************************************************
public class RecursionExercises
{
    public static void main(String[] args) 
    {
        Scanner  scan = new Scanner(System.in);
        int choise;
        boolean fcontinue = true;

        // do while 
        do 
        {
            // menu 
            System.out.println("Please Choose one of the following loops exercises: ");
            System.out.println("1 - For exercise 2");
            System.out.println("2 - For exercise 3");
            System.out.println("3 - For exercise 4");
            System.out.println("4 - For exercise 8");
            System.out.println("5 - For exercise 9");
            System.out.println("6 - For exercise 20");
            System.out.println("7 - For exercise 22");
            System.out.println("0 - To Exit " + "\n");
            System.out.println("Enter your choise --->  ");
            // take input 
            choise = scan.nextInt();
            // switch case 
            switch (choise) 
            {
                case 1: 
                {
                    System.out.println("Enter Number: ");
                    int num = scan.nextInt();
                    System.out.println(countEvenDigits(num));
                    break;
                }// end of case 1
                case 2: 
                {
                    System.out.println("Enter Number: ");
                    int num1 = scan.nextInt();
                    System.out.println(allEvenDigits(num1));

                    break;
                }// end of case 2
                case 3: 
                {	
                    System.out.println("Enter size of the array: ");
                    int size = scan.nextInt();
                    int[] arr = new int[size];
                    for(int i = 0; i < size; i++)
                    {	
                        arr[i] = scan.nextInt();
                    }
                    System.out.println(countEven(arr, size));
                    break;
                }// end of case 3
                case 4: 
                {
                    System.out.println("Enter Number: ");
                    int num2 = scan.nextInt();
                    System.out.println(isAlternating(num2));
                    break;
                }// end of case 4
                case 5: 
                {
                    System.out.println("Enter Number: ");
                    int num3 = scan.nextInt();
                    System.out.println(hasAlternating(num3));
                    break;
                }// end of case 5
                case 6: 
                {
                    System.out.println("Enter Number: ");
                    int num4 = scan.nextInt();
                    System.out.println(calculateTerm(num4));
                    break;
                }// end of case 6
                case 7: 
                {
                    System.out.println("Enter Number: ");
                    int num5 = scan.nextInt();
                    drawRuler(num5);		
                    break;
                }// end of case 7
                case 0: 
                {
                    fcontinue = false;
                    break;			
                }
                default:
                {
                    System.out.println("Invalid option");
                    break;
                }
            }		
        } while (fcontinue);
        System.out.println("Goodbye!!");	
    }// end of method main
    /**
     * method is boolan recursive which returns the num of even digits in a given number 
     * @parm int (num)
     * @return int
     */
    public static int countEvenDigits(int num)
    {
        if (num == 0)
        {
            return 0;
        }
        int lastDigit = num % 10;
        if(lastDigit % 2 == 0)
        {
            return 1 + countEvenDigits(num / 10);
        }
        else
        {
            return countEvenDigits(num / 10);
        }
    }// end of method countEvenDigits

    /**
     * method is boolean recursive which returns true if all the digits in the number is even else false 
     * @parm int num
     * @return boolean 
     */	
    public static boolean allEvenDigits(int num)
    {
        if( num == 0)
        {
            return true;
        }
        int lastDigit = num % 10;
        if(lastDigit % 2 == 0)
        {
            return allEvenDigits(num / 10);
        }
        else
        {
            return false;
        }
    }// end of method allEvenDigits

    /**
     * method is boolean recursive which returns the num of even number in an array of numbers 
     * @parm int[] arr, int index
     * @return int
     */
    public static int countEven(int[] arr, int size)
    {
        if(size == 0)
        {
            return 0;
        }
        int count = 0;
        if(arr[size - 1] % 2 == 0)
        {
            count = 1;
        }
        return count + countEven(arr, size - 1);
    }// end of method countEven

    /**
     * methdo is boolean recursive which returns true if it is an alternation number
     * altenation number is a number in which each pair of adjacent digits has a different parity 
     * @parm int num
     * @return boolean 
     */
    public static boolean isAlternating(int num)
    {
        if (num < 10)
        {
            return true;
        }
        int lastDigit = num % 10;
        int secondLastDigit = (num / 10) % 10;
        if(lastDigit % 2 == secondLastDigit % 2)
        {
            return false;
        }
        else 
        {
            return isAlternating(num / 10);
        }
    }// end of method isAlternating

    /**
     * method is boolean recursive which returns true if there is at least one pair of alternating digits and if the number is a single digit it will return false
     * alternating number is a number in which each pair of adjacent digits has a differnet parity 
     * @parm int num
     * @return boolean 
     */
    public static boolean hasAlternating(int num)
    {
        if(num < 10)
        {
            return false;
        }
        int lastDigit = num % 10;
        int secondLastDigit = (num / 10) % 10;
        if(lastDigit % 2 != secondLastDigit)
        {
            return true;
        }
        else
        {
            return hasAlternating(num / 10);
        }
    }// end of method hasAlternatin

    /**
     * method return the n Term in a sequence 
     * @parm int 
     * @return int
     */
    public static int calculateTerm(int num)
    {
        if(num <= 3)
        {
            return num;
        }
        if(num % 2 == 0)
        {
            return calculateTerm(num -1) + calculateTerm(num - 2) + calculateTerm(num - 3);
        }
        else
        {
            return Math.abs(calculateTerm(num - 1) - calculateTerm(num - 3));
        }
    }// end of method calculateTerm

    /**
     * method is boolean recursive which print a a ruler according to the given num
     * @parm int 
     * @return void
     */
    public static void drawRuler(int num)
    {
        if(num == 0)
        {
            return;
        }
        drawRuler(num - 1);
        for(int i = 0; i < num; i++)
        {
            System.out.print("-");
        }
        System.out.println();
        drawRuler(num -1);
    }// end of method drawRuler
}// end of class RecursionExercises