numberToWords.kt

class NumberToWordConverter {
    private val specialNames = arrayOf("", " thousand", " million", " billion", " trillion", " quadrillion", " quintillion")

    private val tensNames = arrayOf("", " ten", " twenty", " thirty", " forty", " fifty", " sixty", " seventy", " eighty", " ninety")

    private val numNames = arrayOf("", " one", " two", " three", " four", " five", " six", " seven", " eight", " nine", " ten", " eleven", " twelve", " thirteen", " fourteen", " fifteen", " sixteen", " seventeen", " eighteen", " nineteen")

    private fun convertLessThanOneThousand(number: Int): String {
        var number = number
        var current: String

        if (number % 100 < 20) {
            current = numNames[number % 100]
            number /= 100
        } else {
            current = numNames[number % 10]
            number /= 10

            current = tensNames[number % 10] + current
            number /= 10
        }
        if (number == 0) return current
        return numNames[number] + " hundred" + current
    }

    fun convert(number: Int): String {
        var number = number

        if (number == 0) {
            return "zero"
        }

        var prefix = ""

        if (number < 0) {
            number = -number
            prefix = "minus"
        }

        var current = ""
        var place = 0

        do {
            val n = number % 1000
            if (n != 0) {
                val s = convertLessThanOneThousand(n)
                current = s + specialNames[place] + current
            }
            place++
            number /= 1000
        } while (number > 0)

        return (prefix + current).trim { it <= ' ' }
    }
}