object NumberToWords {
/*
Convert numbers to English words in Scala
-----------------------------------------
Supports numbers from 0 to 999,999,999,999,999.
Strategy:
- Break the number into named groups: trillions, billions, millions,
thousands, hundreds.
- Convert each 0–999 group using a helper method.
- Append group names ("trillion", "billion", etc.) when needed.
- Build the final string using a ListBuffer and mkString for efficiency.
*/
private val ones: Vector[String] = Vector(
"zero", "one", "two", "three", "four",
"five", "six", "seven", "eight", "nine",
"ten", "eleven", "twelve", "thirteen", "fourteen",
"fifteen", "sixteen", "seventeen", "eighteen", "nineteen"
)
private val tensWords: Vector[String] = Vector(
"", "", "twenty", "thirty", "forty",
"fifty", "sixty", "seventy", "eighty", "ninety"
)
/*
appendWord:
Adds a word to the output buffer.
*/
private def appendWord(out: scala.collection.mutable.ListBuffer[String], word: String): Unit =
if (word.nonEmpty) out += word
/*
convertHundreds:
Converts numbers from 0 to 999 into words.
*/
private def convertHundreds(n0: Long, out: scala.collection.mutable.ListBuffer[String]): Unit = {
var n: Long = n0
if (n == 0) return
if (n >= 100) {
appendWord(out, ones((n / 100).toInt))
appendWord(out, "hundred")
n %= 100
if (n > 0) appendWord(out, "and")
}
if (n >= 20) {
appendWord(out, tensWords((n / 10).toInt))
if (n % 10 != 0) appendWord(out, ones((n % 10).toInt))
} else if (n > 0) {
appendWord(out, ones(n.toInt))
}
}
/*
numberToWords:
Converts any number from 0 to 999,999,999,999,999 into English words.
*/
def numberToWords(num: Long): String = {
if (num == 0) return "zero"
val out = scala.collection.mutable.ListBuffer[String]()
val trillions: Long = num / 1_000_000_000_000L
val billions: Long = (num / 1_000_000_000L) % 1000
val millions: Long = (num / 1_000_000L) % 1000
val thousands: Long = (num / 1_000L) % 1000
val hundreds: Long = num % 1000
if (trillions > 0) {
convertHundreds(trillions, out)
appendWord(out, "trillion")
}
if (billions > 0) {
convertHundreds(billions, out)
appendWord(out, "billion")
}
if (millions > 0) {
convertHundreds(millions, out)
appendWord(out, "million")
}
if (thousands > 0) {
convertHundreds(thousands, out)
appendWord(out, "thousand")
}
if (hundreds > 0) {
convertHundreds(hundreds, out)
}
out.mkString(" ")
}
/*
main:
Demonstrates usage with multiple test numbers.
*/
def main(args: Array[String]): Unit = {
val tests: Vector[Long] = Vector(
1_234,
12_345,
123_456,
1_234_567,
123_456_789,
12_345_678_901L,
1_234_567_890_123L,
999_999_999_999_999L
)
tests.foreach(n => println(s"$n -> ${numberToWords(n)}"))
}
}
/*
run:
1234 -> one thousand two hundred and thirty four
12345 -> twelve thousand three hundred and forty five
123456 -> one hundred and twenty three thousand four hundred and fifty six
1234567 -> one million two hundred and thirty four thousand five hundred and sixty seven
123456789 -> one hundred and twenty three million four hundred and fifty six thousand seven hundred and eighty nine
12345678901 -> twelve billion three hundred and forty five million six hundred and seventy eight thousand nine hundred and one
1234567890123 -> one trillion two hundred and thirty four billion five hundred and sixty seven million eight hundred and ninety thousand one hundred and twenty three
999999999999999 -> nine hundred and ninety nine trillion nine hundred and ninety nine billion nine hundred and ninety nine million nine hundred and ninety nine thousand nine hundred and ninety nine
*/
