Question

In java, please complete the methods in the class below. Add comments to identify your base case or base cases and the recursive steps in each of the recursive implementations.

a. public String starsRecursive(int numOfLinesOfStars) takes the number of lines of stars to be in the returned string. The first line will have as many stars as numOfLinesOfStars. Each line after the first line will have one less star. The last line will have only one star. If the value of numOfLinesOfStars is zero or negative, then no starts are produced. This method must be implemented recursively.

e.g. System.out.println(A6.starsRecursive(6));

******
*****
****

***

**

*

b. public String starsIterative(int numOfLinesOfStars) takes the number of lines of stars to be in the returned string. The first line will have as many stars as numOfLinesOfStars. Each line after the first line will have one less star. The last line will have only one star. If the value of numOfLinesOfStars is zero or negative, then no starts are produced. This method must be implemented iteratively.

e.g. System.out.println(A6.starsIterative(6));

******
*****
****

***

**

*

c. public String reverseAndAddCommasRecursive(String wordToReverse) takes a string, reverses characters of the string while inserting commas between each characters. This method must be implemented recursively.

e.g.

System.out.println(A6.reverseAndAddCommasRecursive("cat")); ,t,a,c

d. public String reverseAndAddCommasIterative(String wordToReverse) takes a string, reverses characters of the string while inserting commas between each characters. This method must be implemented iteratively.

e.g.
System.out.println(A6.reverseAndAddCommasIterative ("cat")); ,t,a,c

e. public int multiplyOddIntegersOnlyRecursive(int highestIntInSequence) takes an integer value and multiples all the odd integers between 1 and highestIntInSequence. It returns the result of the multiplication of the odd integers. This method must be implemented recursively.

e.g. System.out.println(A6.multiplyOddIntegersOnlyRecursive(15));

2027025

f. public int multiplyOddIntegersOnlyIterative(int highestIntInSequence) takes an integer value and multiples all the odd integers between 1 and highestIntInSequence. It returns the result of the multiplication of the odd integers. This method must be implemented iteratively.
e.g. System.out.println(A6.multiplyOddIntegersOnlyIterative(15));

2027025

Driver:

package driver;

import assignment6.Assign6;

public class A6Driiver {

public static void main(String[] args) {

Assign6 A6 = new Assign6();

System.out.println("\nPrinting stars recursively:\n"+A6.starsRecursive(6));

System.out.println("\nPrinting stars iteratively:\n"+A6.starsIterative(6));

System.out.println("\nPrinting reverse with commas recursively:\n"+A6.reverseAndAddCommasRecursive("cat"));

System.out.println("\nPrinting reverse with commas iterativey:\n"+A6.reverseAndAddCommasIterative("dogs"));

System.out.println("\nPrinting multiply odd ints only recursively:\n"+A6.multiplyOddIntegersOnlyRecursive(15));

System.out.println("\nPrinting multiply odd ints only iteratively:\n"+A6.multiplyOddIntegersOnlyIterative(15));

}

}

Example output from A6Driver shown below:

Printing stars recursively:
******
*****
****

***

**

*

Printing stars iteratively:
******
*****
****

***

**

*

Printing reverse with commas recursively:
,t,a,c

Printing reverse with commas iterativey:
,s,g,o,d

Printing multiply odd ints only recursively:
2027025

Printing multiply odd ints only iteratively:
2027025

Answer 1

I have written the complete java code with the above 6 functions implemented.

For the multiply integers using recursion, i have used methods to convert string to integer and integer to string as the return type of the given function is string but we need to return the integer values.

Note: You may look the screenshot of the code to have better understanding of the indentation.

Java Code:

package recursion_iteration_functions;

class Assign6
{

   public String starsRecursive(int i) {
       //base case
       if(i <= 0)
           return "";
       else //else print i number of stars
       {
           for(int j=0;j<i;j++)
               System.out.print("*");
           System.out.println(); //new line
           this.starsRecursive(i-1);
       }
       return "";
   }

   public String starsIterative(int i) {
       int n = i;
       for(int u=0;u<i;u++)
       {
           for(int j=0;j<n;j++)
               System.out.print("*");
           System.out.println(); //new line
           n--;
       }
       return "";
   }

   public String reverseAndAddCommasRecursive(String string) {
       //base case- empty string
       if(string.length() == 0)
           return "";
       else
       {
           int n = string.length();
           //System.out.print(",");
           System.out.print(","+string.charAt(n-1));
           //System.out.println("String is: "+string.substring(0,n-1));
           reverseAndAddCommasRecursive(string.substring(0,n-1));
           return "";
       }
   }
  
   public String reverseAndAddCommasIterative(String string) {
       int len = string.length(); //length of string
       for(int i=len-1;i>=0;i--)
       {
           System.out.print(","+string.charAt(i));
       }
       System.out.println(); //new line
       return "";
   }

   public String multiplyOddIntegersOnlyRecursive(int i) {
       //base case
       if(i==1)
       {
           return "1";
       }
       else
       {
           if(i%2 == 0) //check if even number is send
               i--;
           //convert string to long then multiply numbers and
           //then again convert back result to string to return
           //as the return type is string
           return Integer.toString(i*Integer.parseInt(multiplyOddIntegersOnlyRecursive(i-2)));
       }
   }

   public String multiplyOddIntegersOnlyIterative(int i) {
       long res = 1; //stores result
       for(int j=1;j<=i;j+=2)
       {
           res = res*j;
       }
       System.out.println(res);
       return "";
   }
  
}

public class A6Driiver {
  
   public static void main(String[] args) {

       Assign6 A6 = new Assign6();

       System.out.println("\nPrinting stars recursively:");
       A6.starsRecursive(6);

       System.out.println("\nPrinting stars iteratively:");
       A6.starsIterative(6);

       System.out.println("\nPrinting reverse with commas recursively:");
       A6.reverseAndAddCommasRecursive("cat");

       System.out.println("\nPrinting reverse with commas iterativey:");
       A6.reverseAndAddCommasIterative("dogs");

       String res = A6.multiplyOddIntegersOnlyRecursive(15);
       System.out.println("\nPrinting multiply odd ints only recursively:\n"+res);
      

       System.out.println("\nPrinting multiply odd ints only iteratively:");
       A6.multiplyOddIntegersOnlyIterative(15);

       }
}

Output:

Screenshot of code: