Core Java - Interview Questions and Answers for 'Recursion' | Search Interview Question

Core Java - Interview Questions and Answers for 'Recursion' - 12 question(s) found - Order By Newest

Very frequently asked in HCL Tech ( Based of 4 inputs )

Q1. Write a Program to reverse a string iteratively and recursively

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

Strategy - Loop through each character of a String from last to first and append the character to StringBuilder / StringBuffer

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

Strategy - Call the method with substring starting from 2nd character recursively till we have just 1 character.

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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Q2. What will happen if we don't have termination statement in recursion ?

Ans. Function call allocates a stackframe in stack. Every stackframe will use some memory to store local variables, parameters and to remember return address. Without terminating condition stackframes will keep consuming memory from stack and eventually program will result in stackoverflow error.

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Q3. Write a Program to print factorial of a number using recursion

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
System.out.println(factorial(5));
}

private static int factorial(int number){
if(number == 1){
return 1;
} else {
return number * factorial(number - 1);
}
}
}

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Q4. Write a program to calculate factorial of a number using recursion

Core Java

Ans.

public class Factorial {
   public static void main(String[] args){
      int x = 5;

      System.out.println(calculateFactorial(x));

   }

   private static int calculateFactorial(int x){
      if(x==1){
         return 1;
      }
      return x * calculateFactorial(x-1);
   }
}

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Q5. Write an Algorithm for Graph Traversal ? The Graph has a loop.

Algorithm

Ans. Please not that all such questions can be easily answered through recursion.

Simple recursive implementation could be

traverse(root);

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
System.out.println(element);
}
}

but this algo / code lead to endless loop if there is a loop in graph traversal.

So you can keep a collection to keep track of which elements have laready been traversed

static List<Elements> listOfAlreadyTraversedElements = new ArrayList<Elements>();

main(){
traverse(root);
}

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
listOfAlreadyTraversedElements.add(element);
System.out.println(element);
}
}

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Q6. Write a program to print sum of numbers between the start and end number

For example - Passing start number as 2 and end number as 10, it should print 2+3+4+5+6+7+8+9+10 = 54

Core Java

Ans.
public class BuggyBread {
   public static void main(String args[]) {
       System.out.println(sum(2,10));
   }

   private static int sum(int start,int end){
      if(start > end){
         return 0;
      } else {
         return start + sum(start+1,end);
      }
   }
}

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Q7. Write a program using Recursion to print multiplication of numbers between the start and end number

For example - Passing start number as 2 and end number as 10, it should print 2*3*4*5*6*7*8*9*10 = 3628800

Core Java

Ans.
public class BuggyBread {
   public static void main(String args[]) {
       System.out.println(multiply(2,5));
   }

   private static int multiply(int start,int end){
      if(start > end){
         return 1;
      } else {
         return start * multiply(start+1,end);
      }
   }
}

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Q8. Write a Program to display numbers between 2 numbers using recursion

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       displayNumbersBetween(2,10);
   }

   private static void displayNumbersBetween(int start,int end){
      if(start > end){
         return ;
      } else {
         System.out.println(start);
         displayNumbersBetween(start+1,end);
      }
   }
}

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Q9. Write a Program to print asterix like following using Recursion

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

Program should set the start and end index and then display this accordingly. For example the above pattern is for displayNumbersBetween(2,10) and following is for displayNumbersBetween(5,7)

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

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
       displayNumbersBetween(5,7);
   }

   private static void displayNumbersBetween(int start,int end){
      if(start > end){
         return ;
      } else {
         for(int x=1;x<=start;x++){
            System.out.print("*");
         }
         System.out.println("");
         displayNumbersBetween(start+1,end);
      }
   }
}

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Q10. What will happen if we don't have termination statement in recursion ?

Core Java

Ans. It would result in endless function calls and hence eventually would result in stackoverflow exception.

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Q11. Which of the two - iteration or recursion - is slower ?

Core Java

Ans. Any function call is slower than the code in the same method as Java has to maintain stack of meta and function call information. So recursion is slower.

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Q12. Write a Program to print fibonacci series using recursion.

Core Java

Ans. public class FibonacciUsingRecursion {
   public static void main(String[] args) throws IOException{
      getNextFibanocci(1,1);
   }

   static int getNextFibanocci(int a,int b){
      if(a+b >= 100){
         return 0;
      } else {
         System.out.println(a+b);
         getNextFibanocci(b,a+b);
      }

      return 0;
   }
}

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