Find factorial of number in java – recursive & iterative (example)

What is factorial of number?

• Factorial of a non-negative integer n, denoted by n!.
• Factorial is the product of all positive integers less than or equal to n.
  • 0! = 1
  • 1!  = 1
  • 3! = 3 * 2 * 1 = 6
  • 6! = 6 * 5 * 4 * 3 * 2 * 1 = 120
  • n! = n * n – 1! = n * n – 1 * n – 2 ! and so on
• We would like to find factorial of a  given number using recursive & iterative algorithm in java.

Algorithm to find factorial using recursive algorithm

1. Calculate then factorial of number = 5.
2. We know 0! = 1, our base condition.
3. Also, We know n! = n * n – 1! = n * n – 1 * n – 2 ! and so on
4. Find factorial using point 3.
   • i.e. factorial (n) = n * factorial (n-1)
   • factorial (5) = 5 * factorial (4)
     • 5 * 4 * factorial (3).
       • 5 * 4 * 3 * factorial (2).
         • 5 * 4 * 3 * 2 * factorial (1) = 120.
5. We have shown the demonstration of recursive algorithm in Fig 1.

Program to find factorial using recursive & iterative algorithm

package org.learn;

import java.util.Scanner;

public class DemoFactorial {
    private static int factRecursive(int number) {
        // base condition
        if (number == 1)
            return 1;

        // calculate the factorial of all number
        return number * factRecursive(number - 1);
    }

    private static int factIterative(int number) {

        int factorial = 1;
        for (int iNumber = 1; iNumber <= number; iNumber++) {
            factorial = factorial * iNumber;
        }
        return factorial;
    }

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

            /* Calculate factorial for input number */
            System.out.printf(" Enter input number : ");
            int number = scanner.nextInt();

            int factNumber = factRecursive(number);
            System.out.printf("factorial(%d) - Recursive method: %d\n",number,factNumber);

            factNumber = factIterative(number);
            System.out.printf("factorial(%d) - Iterative method: %d\n",number,factNumber);
        }
    }
}

Output: Factorial of a number – recursive & iterative method is:

Enter input number : 5
factorial(5) - Recursive method: 120
factorial(5) - Iterative method: 120

Enter input number : 7
factorial(7) - Recursive method: 5040
factorial(7) - Iterative method: 5040