ISC Class 12th Computer Science Chapter 10 - Recursion Important Questions with Answers

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Give one reason, why iteration is better than recursion.

Question 2.

Differentiate between direct recursion and indirect recursion.

Question 3.

A class Fibo has been defined to generate the Fibonacci series 0, 1, 1, 2, 3, 5, 8, 13, ……. (Fibonacci series are those in which the sum of the previous two terms is equal to the next term).

Some of the members of the class are given below:

Class name	Fibo
Data member/instance variable:
start	integer to store the start value
end	integer to store the end value
Member functions/methods:
Fibo( )	default constructor
void read( )	to accept the numbers
int fibo(int n)	return the nth term of a Fibonacci series using recursive technique
void display( )	displays the Fibonacci series from start to end by invoking the function fibo()

Specify the class Fibo, giving details of the Constructor, void read( ), int fibo(int), and void display( ). Define the main() function to create an object and call the functions accordingly to enable the task.

Question 4.

A class Gcd has been defined to find the Greatest Common Divisor of two integer numbers. Some of the members of the class are given below:

Class name	Gcd
Data member/instance variable:
num1	integer to store the first number
num2	integer to store the second number
Member functions/methods:
Gcd( )	default constructor
void accept( )	to accept the numbers
int gcd(int x,int y)	return the GCD of the two numbers x and y using recursive technique
void display( )	displays the result with an appropriate message

Specify the class Gcd, giving details of the Constructor, void accept( ), int gcd(int,int), and void display( ). Define the main() function to create an object and call the functions accordingly to enable the task.

Question 5.

Assertion: Recursive data structure follows the LIFO principle.

Reason: Execution of recursive code follows the concepts of data structure Queue.

Both Assertion and Reason are true, and Reason is the correct explanation for the Assertion.

Both Assertion and Reason are true, but Reason is not the correct explanation for the Assertion.

Assertion is true but Reason is false.

Assertion is false but Reason is true.

Question 6.

The following function is a part of some class:

int jolly(int[] x, int n, int m)
  {
if (n<0)
  return m;
else if(n<x.length)
  m=(x[n]>m)?x[n]:m;
return jolly(x, --n, m);
  }

What will be the output of jolly() when the value of x[ ]={6,3,4,7,1}, n=4 and m=0?
What function does jolly() perform, apart from recursion?

Question 7.

Design a class DeciHex to accept a positive integer in decimal number system from the user and display its hexadecimal equivalent.

Example 1:

Decimal number= 25

Hexadecimal equivalent= 19

Example 2:

Decimal number =28

Hexadecimal equivalent = 1C

Some of the members of the class are given below.

Class name	DeciHex
Data members/instance variables:
num	stores the positive integer
hexa	string to store the hexadecimal equivalent of num
Methods / Member functions:
DeciHex()	constructor to initialise the data members with legal initial values
void getNum()	to accept a positive integer
void convert(int n)	to find the hexadecimal equivalent of the formal parameter 'n' using the recursive technique
void display()	to display the decimal number and its hexadecimal equivalent by invoking the function convert()

Specify the class DeciHex giving details of the constructor( ), void getNum( ), void convert(int) and void display(). Define a main() function to create an object and call all the functions accordingly to enable the task.

Question 8.

Assertion: Recursion utilises more memory as compared to iteration.

Reason: Time complexity of recursion is higher due to the overhead of maintaining the function call stack.

Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

Assertion is true and Reason is false.

Assertion is false and Reason is true.

Question 9.

The following is a function of class Armstrong. This recursive function calculates and returns the sum of the cubes of all the digits of num, where num is an integer data member of the class Armstrong.

[A number is said to be Armstrong if the sum of the cubes of all its digits is equal to the original number].

There are some places in the code marked by ?1?, ?2?,?3? which may be replaced by a statement/expression so, that the function works properly.

public int sumOfPowers(int num) 
  {
     if(num == 0) 
        return ?1?
     int digit = ?2?;
        return(int)Math.pow(digit, 3) + ?3?;
}

What is the expression or statement at ?1?
What is the expression or statement at ?2?
What is the expression or statement at ?3?

Question 10.

A class LCM has been defined to find the Lowest Common Multiple of two integers.

Some of the data members and member functions are given below:

Class name	LCM
Data members/instance variables:
n1	to store an integer number
n2	to store an integer number
large	integer to store the largest from n1,n2
sm	integer to store the smallest from n1,n2
l	to store lcm of two numbers
Methods / Member functions:
LCM( )	default constructor to initialize data members with legal initial values
void accept()	to accept n1 and n2
int getLCM()	returns the lcm of n1 and n2 using the recursive technique
void display( )	to print the numbers n1, n2 and lcm

Specify the class LCM giving details of the constructor( ), void accept( ), int getLCM() and void display( ). Define a main ( ) function to create an object and call the member functions accordingly to enable the task.