Write a Kotlin Program to Find nth Armstrong Number

What is Armstrong Number ?

A positive integer (x) of n digits is called armstrong number of order n (number of digits in x) if

abcd... = pow(a,n) + pow(b,n) + pow(c,n) + pow(d,n) + ....

Note that abcd… is number x where a, b, c, d ….etc. are it’s digits. n is number of digits in x.

For example,

Input:
9

Output:
9th armstrong number is 9

Input:
10

Output:
10th armstrong number is 153

Input:
15

Output:
15th armstrong number is 8208

1. Program to Find nth Armstrong Number

Sourcecode –

import java.util.*
import kotlin.math.floor
import kotlin.math.log10
import kotlin.math.pow
import kotlin.math.roundToInt

fun main() {
    val read = Scanner(System.`in`)

    println("Enter n:")
    val n = read.nextInt()

    if(n < 1)
        return

    var count = 0
    var armN = 0

    // Run a loop from 1 to INT_MAX to find nth Armstrong number
    for(i in 1..Int.MAX_VALUE) {
        if(checkArmstrong((i))) {
            count++
        }
        if(count == n) {
            armN = i
            break
        }
    }

    if(armN != 0) {
        println("" + n + "th armstrong number is $armN")
    } else {
        println("No " + n + "th armstrong number")
    }
}

private fun checkArmstrong(number: Int): Boolean {

    // Get the count of digits in number
    val n = floor(log10(number.toDouble()) + 1).roundToInt()

    var x = number

    // Find sum by power last digit in n to count.
    var sum = 0
    while(x > 0) {
        val digit = x % 10
        sum = (sum + (digit.toDouble().pow(n))).roundToInt()
        x /= 10
    }

    // Return true if sum is equal to number
    return sum == number
}

When you run the program, output will be –

Enter n:
14
14th armstrong number is 1634

Explanation:

Here, we have created an object of Scanner. Scanner takes an argument which says where to take input from.
System.`in` means take input from standard input – Keyboard.

read.nextIn() means read anything entered by user before space or line break from standard input – Keyboard.

Run a loop from 1 to maximum possible value.
Check for each value (i) if it is an armstrong number. If yes, increase the count.
Compare if count is equal to number n (entered by user). If yes, return value of i.

Thus, we went through Kotlin Program to Find nth Armstrong Number.