Kotlin Program to Find Factorial of a Number Using Recursion

Calculating the factorial of a number is a common problem in computer science and mathematics. Factorials are used in permutations, combinations, and other mathematical computations. In this article, we will explore Kotlin Program to Find Factorial of a Number Using Recursion. Each example will be followed by its output and explanation.

Introduction

The factorial of a non-negative integer 𝑛n is the product of all positive integers less than or equal to 𝑛n. It is denoted by 𝑛!n! and is defined as:

Example 1: Basic Recursion

fun factorial(n: Int): Int {
    return if (n == 0) 1 else n * factorial(n - 1)
}

fun main(args: Array<String>) {
    val number = 5
    val result = factorial(number)
    println("Factorial of $number is $result")
}

1.2 Output

Factorial of 5 is 120

1.3 Explanation

In this example, the factorial function uses a simple recursive approach. If 𝑛n is 0, it returns 1. Otherwise, it returns 𝑛n multiplied by the factorial of 𝑛−1n−1. This is a straightforward implementation of the mathematical definition of factorial.

Example 2: Tail Recursion

tailrec fun factorialTailRec(n: Int, accumulator: Int = 1): Int {
    return if (n == 0) accumulator else factorialTailRec(n - 1, accumulator * n)
}

fun main(args: Array<String>) {
    val number = 6
    val result = factorialTailRec(number)
    println("Factorial of $number is $result")
}

2.2 Output

Factorial of 6 is 720

2.3 Explanation

The factorialTailRec function uses tail recursion to calculate the factorial. The tailrec modifier tells the Kotlin compiler to optimize the recursive calls, preventing stack overflow for large inputs. The function uses an accumulator to carry the intermediate results, making the recursion tail-recursive.

Example 3: Recursive Factorial with Input Validation

3.1 Code

fun factorialWithValidation(n: Int): Int {
    require(n >= 0) { "Number must be non-negative" }
    return if (n == 0) 1 else n * factorialWithValidation(n - 1)
}

fun main(args: Array<String>) {
    val number = 7
    val result = factorialWithValidation(number)
    println("Factorial of $number is $result")
}

3.2 Output

Factorial of 7 is 5040

3.3 Explanation

In this example, the factorialWithValidation function includes input validation to ensure that the input number is non-negative. If the input is negative, it throws an IllegalArgumentException. This helps in making the function more robust by handling invalid inputs gracefully.

Conclusion

We have discussed three different approaches to find the factorial of a number using recursion in Kotlin:

1. Basic Recursion: A straightforward recursive implementation.
2. Tail Recursion: An optimized version using the tailrec modifier to prevent stack overflow.
3. Recursive Factorial with Input Validation: A robust implementation with input validation.

Each method has its advantages and can be chosen based on the requirements of the problem at hand. Understanding these different approaches helps in writing efficient and safe recursive functions in Kotlin.