Clever Geek Handbook

Factorial using a `for` loop in Kotlin

With Java programming experience, I started learning Kotlin today. I am playing around with the language and found I was stuck to find the factorial using a loop for

in kotlin. I managed to do this using a loop while

.

import java.util.Scanner

fun main(args: Array<String>){
    val reader=Scanner(System.`in`)
    val x: Int = reader.nextInt()
    println(factorial(x))
}

fun factorial(a: Int): Int{
    var ans=1
    var i: Int = a
    while(i>1){
        ans*=i
        i--
    }
    return ans
}

Please help me to do this using a loop for

.

thank

+3


source to share


5 answers


Well, the simplest that comes to mind:



fun factorial(num: Int): Long {
    var result = 1L
    for (i in 2..num) result *= i
    return result
}
+10


source


This doesn't use a for loop, but as an addition, you can also make it shorter, more functional, and Kotlin-like using reduce

:

fun factorial(num: Int) = (1..num).reduce(Int::times)

Or:

fun factorial(num: Int) = (1..num).reduce { a, b -> a * b }

This is the simplest I can think of.



Edit: this is equivalent to

fun factorial(num: Int) = (2..num).fold(1, Int::times)

as reduce

is practically a fold

, starting at the value at index 0.

We'll start with 2 instead, however 1 will be equivalent since multiplying by one will not change the result.

Edit 2: This edit is exactly what was just posted in holi java.

+4


source


there is another expressive one using Range # fold and a function reference expression like:

fun factorial(n: Int) = (2..n).fold(1L, Long::times)
+2


source


If I am brave enough not to do it in a for loop,

Here's a handy recursive function to determine the factorial:

fun factorial(a: Int): Long = if (a == 1) a.toLong() else factorial(a - 1) * a
0


source


Factorial:

fun factorial(num : Long) : Long {
    var factorial : Long = 1
    for (i in 2..num) {
        factorial *= i
    }
    println("Factorial of $num = $factorial")
}

Factorial using BigInteger variable:

fun factorial(num : Long) : Long {
    var factorial = BigInteger.ONE
    for (i in 2..num) {
        factorial = factorial.multiply(BigInteger.valueOf(num))
    }
    println("Factorial of $num = $factorial")
}
0


source






More articles:


All Articles