DSA Assignment-3

Question 1: Write a Java program to read your lucky number from the keyboard. Treat –ve no. as NumberFormatException. Write appropriate Exceptional handler.
Solution:

import java.util.*;;

public class Q1 {

	int x;

	public void input(int x)

	{

		this.x=x;

		if(x<0) 

			throw new NumberFormatException("You entered negative number ");

		else

			System.out.println("Your lucky Number: "+x);

	}

	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		int n=0;

		System.out.print("Enter your lucky number: ");

		n=sc.nextInt();

		Q1 ob=new Q1();

		try 

		{	

			ob.input(n);

		}

		catch(Exception e)

		{

			System.out.println("Error "+e);

		}

	}

}

Output:

Enter your lucky number: -5


Error java.lang.NumberFormatException: You entered negative number 



Question 2:Assign your favorite colors in an array. Identify 2 exceptions that may be generated & write exceptional handler in Java.
Solution:	
import java.util.*;

public class Q2 {

	   public void insert(String colour[])throws ArrayIndexOutOfBoundsException

	   {

		   colour[colour.length]="Black";

	   }

       public void display(String colour[])

       {

    	   System.out.println("Selected colours are:");

    	   for(int i=0;i<colour.length;i++)

           {

           	System.out.print(colour[i]+", ");

           }

       }

       public void StringToInt(String colour[])

       {

    	   throw new NumberFormatException("Cannot convert String to int ");

       }

	public static void main(String[] args) {

        String colour[]={"Red","Blue","Yellow","Green"};

        Q2 ob=new Q2();

        ob.display(colour);

        try

        {

            ob.insert(colour);

        }

        catch(Exception e)

        {

        	System.out.println("\nError "+e);

        }

        try

        {

        	ob.StringToInt(colour);	

        }

        catch(Exception e)

        {

        	System.out.println("\nError "+e);

        }

    }

}

Output:

Selected colours are:

Red, Blue, Yellow, Green, 

Error java.lang.ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 4


Error java.lang.NumberFormatException: Cannot convert String to int 


Question 3: Create a class Student & enter mark, name of the student. If mark is more than 100, create exception MarksOutOfBoundException & throw it using Java.
import java.util.Scanner;

class Student{

	  int marks; String name;

	  public Student(int marks,String name)throws Exception

	  {

		  this.marks=marks;

		  this.name=name;

		  if(marks<0 || marks>100)

		  {

			  throw new MarksOutOfBoundsException("Invalid Marks");

		  }

		  else{this.marks=marks;}

	  }

	  public void display()

	  {

		  System.out.println("Your name: "+this.name+"\tYour marks: "+this.marks);

	  }

}

	  class MarksOutOfBoundsException extends Exception

	  {

		  public MarksOutOfBoundsException(String str)

		  {

			  super(str);

		  }

      }

public class Q3 {

	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		System.out.print("Your name: ");

		String s=sc.next();

		System.out.print("Enter marks: ");

		int m=sc.nextInt();

		try

		{

			Student S=new Student(m,s);

			S.display();

		}

		catch(Exception e)

		{

			System.out.println("Error "+e);

		}

	}

}

Output:

Your name: Surajit

Enter marks: 110


Error MarksOutOfBoundsException: Invalid Marks

Question 4. Write a simple main class in Java that contains an experiment that uses the generic Box<T> class to build boxes with different types and that verifies that this class works as advertised. Your experiment should include the following:
Create a boxed String object and two variables that refer to that box. Change the contents of one and determine the effect on the other.
Create a boxed Integer object and two variables that refer to that box. Change the contents of one and determine the effect on the other.
Create a boxed Object object and two variables that refer to that box. Determine what happens if you put a string in the box. Determine what happens if you put an integer in the box.
class Box<T> {

    public T content;



    public Box(T content) {

        this.content = content;

    }



    public T getContent() {

        return content;

    }



    public void setContent(T content) {

        this.content = content;

    }

}



public class Q5 {

    public static void main(String[] args) {

        // Create a boxed String object

        Box<String> stringBox = new Box<>("Hello, World!");



        // Create two variables that refer to the same string box

        Box<String> variable1 = stringBox;

        Box<String> variable2 = stringBox;



        // Change the contents of one variable

        variable1.setContent("Modified content");



        // Verify the effect on the other variable

        System.out.println("Variable 2 content: " + variable2.getContent());



        // Create a boxed Integer object

        Box<Integer> intBox = new Box<>(42);



        // Create two variables that refer to the same integer box

        Box<Integer> intVariable1 = intBox;

        Box<Integer> intVariable2 = intBox;



        // Change the contents of one variable

        intVariable1.setContent(99);



        // Verify the effect on the other variable

        System.out.println("Int variable 2 content: " + intVariable2.getContent());



        // Create a boxed Object object

        Box<Object> objectBox = new Box<>(null);



        // Put a string in the object box

        objectBox.setContent("This is a string");



        // Verify the content

        System.out.println("Object box content (String): " + objectBox.getContent());



        // Put an integer in the object box

        objectBox.setContent(123);



        // Verify the content

        System.out.println("Object box content (Integer): " + objectBox.getContent());

    }

}

Output:
Variable 2 content: Modified content
Int variable 2 content: 99
Object box content (String): This is a string
Object box content (Integer): 123

Question 5: Write a java program to print an array of different type using a single Generic method. The signature of printArray method is given below. 
    public static < E > void printArray( E[] inputArray)
public class Q5 {

	public static < E > void printArray( E[] inputArray)

	{

		for(int i=0;i<inputArray.length ;i++) {

			System.out.print(inputArray[i]+" ");

		}

		System.out.println();

	}

	public static void main(String[] args) {

       Integer arr[]= {1,2,3,4,5};

       printArray(arr);

       String s[]= {"A","B","C","D","E"};

       printArray(s);

       

	}

 }

Output:
1 2 3 4 5 
A B C D E 

Question 6:Write a Java method using Generics to count the occurrence of an element in an array of any type. The signature of count method is given below. 
       public static int count(T[] array, T item)
Solution:
public class Q6 {

	public static void main(String[] args) {

      Integer arr[]= {1,2,3,4,1,1,1};

      Integer i=1; 

      System.out.println("Occurrence of "+i+" is "+count(arr,i)+" times");

	}

	public static <T>int count(T[] array, T item)

	{

		int c=0;

		System.out.print("[");

		for(int i=0;i<array.length;i++)

		{

			if(array[i]==item)

			{

				c++;

			}

			System.out.print(array[i]+" ");

			}

		System.out.println("]");

		return c;

	}

}

Output:

[1 2 3 4 1 1 1 ]


Occurrence of 1 is 4 times.

Question 7.Write a recursive method in Java that computes the factorial of a given integer.
import java.util.*;

public class Q7 {

	public static int fact(int n)

	{

		if(n==1 || n==0)

		    return 1;

		else

			return n*fact(n-1);

	}

	public static void main(String[] args) {

     Scanner sc=new Scanner(System.in);

     System.out.println("Enter a no: ");

     int n=sc.nextInt();

     System.out.println("Factorial= "+fact(n));

      

	}



}

Output:
Enter a no: 5
Factorial= 120

Question 8.Write a recursive method in Java which, given real value x and a positive integer n, returns the value of x^n
import java.util.*;

public class Q8 {

	public static int pow(int base ,int power)

	{

		if(base==0)

			return 0;

		else if(power==0)

			return 1;

		else

			return base*pow(base,power-1);

	}



	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		System.out.println("Enter the base: ");

		int base=sc.nextInt();

		System.out.println("Enter the power: ");

		int power=sc.nextInt();

	   System.out.println(base+" to the power of "+power+" is "+pow(base,power));

	}



}

Output:
Enter the base: 
2
Enter the power: 
12
2 to the power of 12 is 4096

Question 9.Write a recursive method in Java which, given an integer n, print it with its digits reversed.
 For example , given 4735, it prints 5374.
import java.util.*;

public class Q9 {

	public static String reverse(int n)

	{

		if(n==0)

		 return "";

		else

			return n%10+reverse(n/10);

	

	}

	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		System.out.println("Enter a no. ");

		int n=sc.nextInt();

		System.out.println("Reverse "+reverse(n));

		

	}

}

Alternative Solution:
import java.util.*;

public class Q9 {

	public static int reverse(int n,int sum)

	{

		if(n==0)

			return sum;

		else

		{

			sum=sum*10+n%10;

			return reverse(n/10,sum);

		}

	

	}

	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		System.out.println("Enter a no. ");

		int n=sc.nextInt();

		System.out.println("Reverse "+reverse(n,0));

		

	}

}

Output:
Enter a no. 
2024
Reverse 4202

Question 10. The sequence of numbers 1, 1, 2, 3, 5, 8, 13 etc are called Fibonacci numbers,each is the sum of the preceding two. Write a recursive method in Java which, given n, returns the nth Fibonacci number.
import java.util.*;

public class Q10 {

	public static int fibonacci(int n)

	{

		if(n==0 || n==1)

			return n;

		else

			return fibonacci(n-1)+fibonacci(n-2);

	}



	public static void main(String[] args) {

		Scanner sc=new Scanner(System.in);

		System.out.println("Enter no. of terms ");

		int n=sc.nextInt();

		for(int i=0;i<n;i++) {

		System.out.print(fibonacci(i)+" ");

		}

	}



}

ALTERNATE SOLUTION:
import java.util.*;

public class fibonacci {

public static void printfibonacci(int a,int b,int n) {// a,b,c...n [c=a+b](logic)

	if(n==0 || n==1)

	{

		return ;

	}

	int c=a+b;

	System.out.print(c+" ");

	printfibonacci(b,c,n-1);

  }	

	public static void main(String[] args) {

		// TODO Auto-generated method stub

        Scanner sc=new Scanner(System.in);

        System.out.println("Enter the number of terms: ");

        int n=sc.nextInt();

        int a=0,b=1;

        System.out.print(a+" "+b+" ");

        printfibonacci(a,b,n-2); //We have already printed 2terms 0,1

                                 // so we are writing n-2

	}

}	

Output:
Enter no. of terms 
10
0 1 1 2 3 5 8 13 21 34 

HOME ASSIGNMENT SOLUTIONS :
Question 1. Write a recursive method in Java to return the greatest common divisor(gcd) of two integers m and n, given that in general, gcd(m,n)=gcd(n, m mod n).

import java.util.*;

 class HA_Q1{



      public static int gcd(int m, int n)

 {

    	  if(n==0)

          return m;

          else

          return gcd(n,m%n);



  }

 public static void main(String[] args)



    {

      Scanner sc = new Scanner(System.in);

      System.out.println("Enter the first number: ");

      int m = sc.nextInt();

      System.out.println("Enter the second number: ");

      int n = sc.nextInt();

      System.out.print("GCD between "+m+" and "+n+" is "+gcd(m,n));

     }

 

 }

Output:
Enter the first number: 
12
Enter the second number: 
136
GCD between 12 and 136 is 4

Question 2. Write a recursive method in Java to search an element of an array using binary search.
 import java.util.*;

 class HA_Q2

 {

      public static void BinarySearch(int arr[], int item, int start, int end)

      {

           int mid = (start+end)/2;

           if(start>end)

        	   System.out.println("Search element not found");

           else if(arr[mid] == item)

        	   System.out.println("Search element found");

           else if(arr[mid]>item)

               BinarySearch(arr, item,start, mid-1);

           else

        	   BinarySearch(arr, item, mid+1,end);

       }

 public static void main(String[] args)

 {

     Scanner sc=new Scanner(System.in);

     System.out.println("Enter no. of. elements you want to enter in the array ");

     int n=sc.nextInt();

	 int arr[]=new int[n];

	 for(int i=0;i<n;i++)

	 {

		 System.out.print("Enter "+(i+1)+" element: \n");

		 arr[i]=sc.nextInt();

	 }

	 System.out.println("Enter item you want to search: ");

	 int item=sc.nextInt();

          BinarySearch(arr, item, 0,arr.length-1);

     }

 }

Output:
Enter no. of. elements you want to enter in the array 
5
Enter 1 element: 
100
Enter 2 element: 
150
Enter 3 element: 
200
Enter 4 element: 
250
Enter 5 element: 
300
Enter item you want to search: 
200
Search element found

Question  3. Write a recursive method in Java to find the binary equivalent of a positive decimal integer.
import java.util.*;

public class HA_Q3 {

    public static int findBinary(int d) {

        if (d == 0)

            return 0;

        else

            return (d % 2) + 10 * findBinary(d/2);

    }



    public static void main(String[] args) {

        Scanner sc= new Scanner(System.in);

        System.out.print("Enter a positive decimal number: ");

        int n= sc.nextInt();

        sc.close();

        System.out.println("Binary equivalent: " + findBinary(n));

    }

}

Output:
Enter a positive decimal number: 13
Binary equivalent: 1101

Question  4.Write a recursive method in Java to find the product of 2 numbers.
import java.util.*;

public class HAQ4 {

	public static int product(int m,int n)

	{

		if (m < n)

            return product(n, m); //Swap the numbers if m < n

        else if (n != 0)

            return m + product(m, n - 1); // Recursively calculate n times sum of m

        else

            return 0;

	}

	public static void main(String[] args) {

		 Scanner sc = new Scanner(System.in);

		 System.out.println("Enter the first number: ");

		 int m = sc.nextInt();

		 System.out.println("Enter the second number: ");

		 int n = sc.nextInt();

		 System.out.print("Product of "+m+"x"+n+" is :"+product(m,n));

	}

}

Output:
Enter the first number: 

11

Enter the second number: 

9

Product of 11x9 is :99

Question 5. Write a recursive Java method that takes a character string s and outputs its reverse. For example, the reverse of 'pots&pans' would be 'snap&stop'.
import java.util.*;

public class HAQ5 {

	 public static String reverse(String S, int index)

	 {

	 if(index<S.length())

	 return reverse(S, index+1)+S.charAt(index);

	 else

	 return " ";

	 }

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		 System.out.println("Enter a string: ");

		 String S = sc.nextLine();

		 System.out.println("reverse is: "+reverse(S,0));



	}

}

Output:
Enter a string: 

pots&pans

reverse is:  snap&stop

Question 6. Write a recursive Java method that determines if a string s is a palindrome, that is, it is equal to its reverse. Examples of palindromes include 'racecar' 'gohangasalamiimalasagnahog'
import java.util.*;

public class HAQ6 {

	 public static String reverse(String S, int index)

	 {

	 if(index<S.length())

		 return reverse(S, index+1)+S.charAt(index);

	 else

		 return "";

	 }

	 public static void isPalindrome(String S)

	 {

	 if(S.equals(reverse(S,0)))

	 System.out.println("Palindrome string");

	 else

		 System.out.println("Not Palindrome string");

	 }

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		 System.out.println("Enter a string: ");

		 String S = sc.nextLine();

		 isPalindrome(S);

	}

}

Output:
Enter a string: 
racecar
Palindrome string
Question 7. Given an unsorted array, A, of integers and an integer k, write recursive program using Java for rearranging the elements in A so that all elements less than or equal to k come before any elements larger than k.
import java.util.*;

public class HAQ7 {

	 public static int[] swap(int arr[], int start, int end, int item)

	 {

	 if(start>end)

	 return arr;

	 else if(arr[start]<=item)

	 return swap(arr, ++start, end, item);

	 else if(arr[end]>item)

	 return swap(arr, start,--end, item);

	 else

	 {

		 int temp = arr[start];

		 arr[start] = arr[end];

		 arr[end] = temp;

		 return swap(arr, ++start,--end, item);

	 }

}

 public static void display(int arr[])

	 {

	 for(int i = 0;i<arr.length;i++)

	 {

	 System.out.print(arr[i]+" ");

	 }

}

	public static void main(String[] args) {

		 int arr[]={3, 9, 4, 11, 5, 1, 7};

		 arr = swap(arr,0,arr.length-1,5);

		 display(arr);

	}

}

Output:
3 1 4 5 11 9 7
Question 8. In the Towers of Hanoi puzzle, we are given a platform with three pegs, a, b, and c, sticking out of it. On peg a is a stack of n disks, each larger than the next so that the smallest is on the top and the largest is on the bottom. The puzzle is to move all the disks from peg a to peg c, moving one disk at a time, so that we never place a larger disk on top of a smaller one. See Figure 1 for an example of the case n = 4. Write a recursive program using Java for solving the Towers of Hanoi puzzle for arbitrary n. (Hint: Consider first the subproblem of moving all but the nth disk from peg a to another peg using the third as “temporary storage.”)
public class HAQ8 {

    public static void towerOfHanoi(int n, char fromRod, char toRod, char auxRod) {

        if (n == 1) {

            System.out.println("Move disk 1 from rod " + fromRod + " to rod " + toRod);

            return;

        }

        towerOfHanoi(n - 1, fromRod, auxRod, toRod);

        // Move the nth disk from 'fromRod' to 'toRod'

        System.out.println("Move disk " + n + " from rod " + fromRod + " to rod " + toRod);

        // Move (n-1) disks from 'auxRod' to 'toRod' using 'fromRod' as auxiliary

        towerOfHanoi(n - 1, auxRod, toRod, fromRod);

    }

    public static void main(String[] args) {

        int n = 4; // Number of disks

        towerOfHanoi(n, 'A', 'C', 'B'); // 'A' is the source rod, 'C' is the target rod, 'B' is the auxiliary rod

    }

}

Output:
Move disk 1 from rod A to rod B
Move disk 2 from rod A to rod C
Move disk 1 from rod B to rod C
Move disk 3 from rod A to rod B
Move disk 1 from rod C to rod A
Move disk 2 from rod C to rod B
Move disk 1 from rod A to rod B
Move disk 4 from rod A to rod C
Move disk 1 from rod B to rod C
Move disk 2 from rod B to rod A
Move disk 1 from rod C to rod A
Move disk 3 from rod B to rod C
Move disk 1 from rod A to rod B
Move disk 2 from rod A to rod C
Move disk 1 from rod B to rod C