Interview Programs

1. Program to find whether a given number is even or odd.
public class P1_EvenNumber {
	public static void main(String[] args) {
		int num = 51;

		// using mod(%) which gives us the remainder
		// comparing remainder with zero
		if (num % 2 == 0) {
			System.out.println(num + " : Number is Even");
		} else {
			System.out.println(num + " : Number is Odd");
		}
	}
}
2. Program to find whether a given number is prime or not.
public class P2_PrimeNumber {

	public static void main(String[] args) {

		int num = 23;
		int flag = 0;

		if (num == 1) {
			System.out.println(" 1 is neither prime nor composite");
		} else {
			// check for number less than half of it as it won't be completely divisible by
			// number more than it
			// starting with 2 as 1 is neither prime nor composite
			for (int i = 2; i <= (num / 2); i++) {

				// check divisible by i or not
				// if divisible, then not prime
				if (num % i == 0) {
					flag++;
				}
			}

			if (flag > 0) {
				System.out.println(num + " is not a Prime Number");
			} else {
				System.out.println(num + " is a Prime Number");
			}
		}
	}
}
3. Program to print the first 10 numbers of the Fibonacci Series.
public class P3_FibonacciSeries {

	public static void main(String[] args) {
		
		int i = 0;
		int j = 1;
		int z = 0;
		
		//Print first 10 numbers of fibonacci series
		int count = 10;
		
		System.out.println(i);
		System.out.println(j);
		
		//Adding up values and resetting values of i and j with the latest values(previous)
		for(int k =0; k < count-2; k++) {
			z = i + j;
			i = j;
			j = z;
			System.out.println(z);
		}
	}
}
4. Program to check whether a number is Armstrong number or not.
public class P4_ArmstrongNumber {

	public static void main(String[] args) {
		
		int inputNum = 370;
		int sumOfCube = 0;
		int num = inputNum;
		
		while(num > 0) {
			
			//calculate sumOfCube
			
			//fetch last digit of number by using mod(%)
			int lastDigit = num % 10;
			
			//updating num by removing the last digit
			num = num / 10;
			
			//Add sum of cubes of each digit
			sumOfCube = sumOfCube + (lastDigit * lastDigit * lastDigit);
		}
		if(sumOfCube == inputNum) {
			System.out.println(inputNum + " is an ArmstrongNumber");
		} else {
			System.out.println(inputNum + " is not an Armstrong Number");
		}
	}
}
5. Program to find the factorial of a number.
public class P5_Factorial {

	public static void main(String[] args) {
		
		int num = 5;
		int factorial = 1;
		
		//multiply in decreasing order by decrementing till you reach 1
		// we will apply a reverse loop
		for(int i = num; i > 0; i--) {
			factorial = factorial * i;
		}
		System.out.println("Factorial of " + num + " is : " + factorial);
	}
}
6. Program to find the factorial of a number using recursion.
public class P6_FactorialUsingRecursion {
	
	//Number to check factorial for
	int num = 5;
	
	//Number to store factorial
	int result = 1;

	public static void main(String[] args) {
		FactorialUsingRecursion f = new FactorialUsingRecursion();
		System.out.println(f.fact(f.num));
	}
	
	public int fact(int num) {
		if (num > 0) {
			result = result * num;
			
			//calling recursively
			fact(num-1);
		}
		return result;
	}
}
7. Program to find missing numbers in an array between 1 to 10.
import java.util.Arrays;

public class P7_MissingNumbersInArray {

	public static void main(String[] args) {
		int[] input = { 5, 7, 6, 2 };
		int index = 0;
		Arrays.sort(input);
		
		//Approach 1
		System.out.println("Approach 1");
		System.out.println("----------");
		int limit = input[input.length-1];

		for(int i = 1; i < limit; i++) {
			if(input[index] == i) {
				index++;
			} else {
				System.out.println(i);
			}
		}
		while(limit < 10) {
			System.out.println(++limit);
		}
		
		//Approach 2
		System.out.println("Approach 2");
		System.out.println("----------");
		
		int[] output = new int [11];
		
		for(int i : input) {
			output[i] = 1;
		}
		for(int i=1; i<output.length; i++) {
			if( output[i] == 0) System.out.println(i);
		}
		
	}
}
8. Program to find the reverse of a string.
public class P8_ReverseAString {

	public static void main(String[] args) {
		
		String originalString = "Miss TecHack";
		String reversedString = "";
		
		//convert string to char array
		char[] charArray = originalString.toCharArray();
		
		//Applying a reverse loop
		for(int i = charArray.length-1; i >= 0; i--) {
			
			//appending string in reverse order
			reversedString = reversedString + charArray[i];
		}
		
		System.out.println("Original String : " + originalString);
		System.out.println("Reversed String : " + reversedString);
	}
}
9. Program to find the reverse of a string using recursion.
public class P9_ReverseAStringUsingRecursion {

	String input = "Recursion";
	
	public static void main(String[] args) {
		ReverseAStringUsingRecursion r = new ReverseAStringUsingRecursion();
		System.out.println(r.reverse(r.input));
	}

	public String reverse(String inputString) {
		if(inputString.isEmpty()) {
			return inputString;
		}
		if(inputString.length() > 0) {
			return inputString.charAt(inputString.length()-1) + reverse(inputString.substring(0, inputString.length()-1));
		}
		return null;
	}
}
10. Program to find the reverse of a string using the default method.
public class P10_ReverseAStringUsingDefaultMethod {

	public static void main(String[] args) {
		
		StringBuffer input = new StringBuffer("Buffer");
		System.out.println(input.reverse());
		
		StringBuilder input2 = new StringBuilder("Builder");
		System.out.println(input2.reverse());
	}
}

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