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to Phone Number in the Scala Track

Test suite

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as


where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

  • +1 (613)-995-0253
  • 613-995-0253
  • 1 613 995 0253
  • 613.995.0253

should all produce the output


Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.


For simplicity and readability: Consider using the Scala collection functions instead of Java's String methods. Remember that in Scala a String is implicitly also a Seq[Char], so you can call them as easily as the String methods.

Some examples:

  • filter instead of replaceAll
  • take, takeRight, drop, head, tail instead of substring

Another idea worth exploring might be to change the String into a List[Char] and then use pattern matching with the :: operator.

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.


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import org.scalatest.{Matchers, FunSuite}

/** @version 1.4.0 */
class PhoneNumberTest extends FunSuite with Matchers {

  test("cleans the number") {
    PhoneNumber.clean("(223) 456-7890") should be(Some("2234567890"))

  test("cleans numbers with dots") {
    PhoneNumber.clean("223.456.7890") should be(Some("2234567890"))

  test("cleans numbers with multiple spaces") {
    PhoneNumber.clean("223 456   7890   ") should be(Some("2234567890"))

  test("invalid when 9 digits") {
    PhoneNumber.clean("123456789") should be(None)

  test("invalid when 11 digits does not start with a 1") {
    PhoneNumber.clean("22234567890") should be(None)

  test("valid when 11 digits and starting with 1") {
    PhoneNumber.clean("12234567890") should be(Some("2234567890"))

  test("valid when 11 digits and starting with 1 even with punctuation") {
    PhoneNumber.clean("+1 (223) 456-7890") should be(Some("2234567890"))

  test("invalid when more than 11 digits") {
    PhoneNumber.clean("321234567890") should be(None)

  test("invalid with letters") {
    PhoneNumber.clean("123-abc-7890") should be(None)

  test("invalid with punctuations") {
    PhoneNumber.clean("123-@:!-7890") should be(None)

  test("invalid if area code starts with 0") {
    PhoneNumber.clean("(023) 456-7890") should be(None)

  test("invalid if area code starts with 1") {
    PhoneNumber.clean("(123) 456-7890") should be(None)

  test("invalid if exchange code starts with 0") {
    PhoneNumber.clean("(223) 056-7890") should be(None)

  test("invalid if exchange code starts with 1") {
    PhoneNumber.clean("(223) 156-7890") should be(None)
object PhoneNumber {
  val Invalid = List("000", "000", "0000")
  val ValidNumber = """1?(\d{3})(\d{3})(\d{4})""".r

class PhoneNumber(rawNumber: String) {
  private val parts = rawNumber.filter(_ isDigit) match {
    case PhoneNumber.ValidNumber(parts @ _*) => parts
    case _ => PhoneNumber.Invalid

  val number = parts.mkString("")
  val areaCode = parts(0)

  override def toString = "(%s) %s-%s".format(parts:_*)

What can you learn from this solution?

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Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
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Community comments

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over 2 years ago
helenst says

Storing the separate parts of the phone number to avoid too much string manipulation.