Update and rename RecursionExercisesAfekaCollege.java to RecursionExercises.java

Author: lironmiz

RecursionExercises.java

@@ -0,0 +1,254 @@
+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