1. program to find the HCF/GCD of 2 numbers without using recursion.

import java.util.Scanner;

public class Solution {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		System.out.print("");
		int a = scanner.nextInt();
		System.out.print("");
		int b = scanner.nextInt();
		
		while (a != b) {
			if(a==0)
			{
				System.out.print(b);
				break;
			}
			if(b == 0)
			{
				System.out.println(a);
			}
			if ( a > b ) {
				a = a - b;
			} else {
				b = b - a; 
			}
		}
		System.out.printla(a);
		scanner.close();
	}
}

2. Write a program to find the factorial of a number.

Factorial of a number nnn is the product of all positive integers less than or equal to nnn. It is denoted as n!n!n!. For example:

5!=5×4×3×2×1=1205! = 5 \times 4 \times 3 \times 2 \times 1 = 1205!=5×4×3×2×1=120
0!=10! = 10!=1 (By definition)

1. Iterative Method (Without Recursion)

import java.util.Scanner;

public class FactorialIterative {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input number
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();

        // Calculate factorial
        long factorial = 1;
        for (int i = 1; i <= num; i++) {
            factorial *= i; // Multiply each number
        }

        // Display result
        System.out.println("The factorial of " + num + " is: " + factorial);

        scanner.close();
    }
}

2. Recursive Method: Recursion ka use tab hota hai jab ek function apne aapko call karta hai.

import java.util.Scanner;

public class FactorialRecursive {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input number
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();

        // Calculate factorial using recursion
        long factorial = findFactorial(num);

        // Display result
        System.out.println("The factorial of " + num + " is: " + factorial);

        scanner.close();
    }

    // Recursive function to calculate factorial
    public static long findFactorial(int n) {
        if (n == 0 || n == 1) {
            return 1; // Base case
        }
        return n * findFactorial(n - 1); // Recursive case
    }
}

3. Given a string of characters followed by their frequency, compress it into a proper format.

Input: a3b5c2a2 Output: abc

Logic

Traverse the input string character by character.
If the current character is a letter:
- Store it as the current character.
If the current character is a digit:
- Extract the frequency of the previous character.
- Append the character to the result string once (ignoring its frequency for compression).
Continue this process until the entire input string is traversed.

Example Walk-through

Input: `a3b5c2a2`

Read a, frequency = 3 → Add a once to the result (a).
Read b, frequency = 5 → Add b once to the result (ab).
Read c, frequency = 2 → Add c once to the result (abc).
Read a, frequency = 2 → Add a once again (abca).

Final output: abc.

import java.util.Scanner;

public class StringCompression {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input string
        System.out.print("Enter the string: ");
        String input = scanner.nextLine();

        // Result string
        StringBuilder result = new StringBuilder();

        // Process the input string
        for (int i = 0; i < input.length(); i++) {
            char ch = input.charAt(i);

            // If the character is a letter, add it to the result once
            if (Character.isLetter(ch)) {
                result.append(ch);
            }
        }

        // Print the compressed string
        System.out.println("Compressed string: " + result.toString());

        scanner.close();
    }
}

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4. palindrome of a string

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