Daily Challenge #9 - What's Your Number?

Can I have your number?

Write a function that accepts an array of 10 integers (between 0 and 9), that returns a string of those numbers in the form of a phone number.

The returned format must be correct in order to complete this challenge.
Don't forget the space after the closing parentheses!

Today's challenge comes from user xDranik on Codewars

Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge for a future post? Email [e-mail] with your suggestions!

Comments

[Frederik 👨‍💻➡️🌐 Creemers]

I think this challenge description is very country specific, as every country has a different way of formatting these.

[Cécile Lebleu]

Could you provide an example? The length and format tends to differ in different countries.
In Costa Rice, for example, it might be 8 or 11 numbers long; as in 8765-4321, or, with the country code, ([phone]. Either way it’s not 10 characters.
Thanks!

[Corey Alexander]

I agree with the other commentors that we need an example in the post to make it easier to understand! Especially with all the different ways telephone numbers are handled country to country.

Luckily the linked Codewars page has an example!

createPhoneNumber([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]) // => returns "[phone]"

[Alvaro Montoro]

JavaScript

I assumed the US phone number format that is (XXX) XXX-XXXX

const formatNumber = numbers => {

  let phoneNumber = "";

  // prerequisites:
  //   - input must be an array
  //   - with 10 elements
  //   - each element will be a single digit number
  if (
    Array.isArray(numbers) &&
    numbers.length === 10 &&
    numbers.every(n => n > -1 && n < 10)
  ) {
    // break the phone number into parts and generate the formmated string
    const areaCode = numbers.slice(0,3).join('');
    const firstPart = numbers.slice(3,6).join('');
    const secondPart = numbers.slice(6).join('');
    phoneNumber = `(${areaCode}) ${firstPart}-${secondPart}`;
  }

  return phoneNumber;
}

Live demo on CodePen (with an alternative version in one line).

[Avery]

Why the one line solution?

[Alvaro Montoro]

No real reason. Both do the same, the first one is more verbose and easier to understand. I deleted the one-line one to avoid any confusion.

[Jaime López]

That's not the first time a challenge is not well explained. You need to grab the whole problem description here to let people give possible solutions. I like these challenges but need a good and clear description of the problem, why don't connect to codewars directly?

[Dylan Paulus]

Nim

import strutils
from sequtils import map

const phone_number = @[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

proc createPhoneNumber(numbers: seq[int]): string =
  if len(numbers) < 10:
    raise newException(ValueError, "invalid length provided to createPhoneNumber(), requires 10 digits")

  return "($#$#$#) $#$#$#-$#$#$#$#" % numbers.map(proc (p: int): string = intToStr(p))



# Run
echo createPhoneNumber(phone_number)

[Yozen Hernandez]

Well I think I've found my new language I want to learn.

[Steven]

python3

#!/usr/bin/env python3


def createPhoneNumber(array_of_integers):
    return "(%s%s%s) %s%s%s-%s%s%s%s" % tuple(array_of_integers)


if __name__ == '__main__':
    print(createPhoneNumber([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]))

[Fernando B 🚀]

I am not a big fan of code challenges in this format. For one people can see other answers. That can skew your thinking before even attempting the challenge. Secondly I think you should submit your own answers on codewars, and then link it here. Only people that has passed the challenge would be able to see it.

@ben definitely need a spoiler tag.

[E. Choroba]

#! /usr/bin/perl
use warnings;
use strict;

sub phone_num {
    local $" = "";
    "(@_[0 .. 2]) @_[3..5]-@_[6..9]"
}

use Test::More tests => 1;
is phone_num(0 .. 9), '[phone]';

The special variable $" is used to separate arrays interpolated in double quotes. By default, it contains a space, but we need the numbers to be adjacent, so we set it locally (i.e. in a dynamic scope) to an empty string.

Another possible short solution is

sub phone_num {
    "[phone]" =~ s/(\d)/$_[$1]/gr
}

The substitution replaces each digit in the template string with the corresponding element of the @_ array which keeps the list of the subroutine arguments. /g means "global", it's needed to replace all the digits, not just the first one. The /r means "return" - normally, a substitution changes the bound left-hand side value, but with /r, it just returns the value.

[Yozen Hernandez]

Nice, basically what I got. sprintf works as well.

#!/usr/bin/env perl

use strict;
use warnings;

sub createPhoneNumber {
    sprintf "(%s%s%s) %s%s%s-%s%s%s%s", @_;
    # local $" = "";
    # "(@_[0..2]) @_[3..5]-@_[6..9]";
}

print createPhoneNumber(1, 2, 3, 4, 5, 6, 7, 8, 9, 0) . "\n";

The regex solution was pretty interesting. Thanks for the explanation!

[Corey Alexander]

My Rust Solution and test cases!

I felt this one was a little easier than some of the previous days, but nothing wrong with that!

#[derive(Debug, PartialEq)]
pub enum Error {
    InvalidLength,
    NotSingleDigitInput,
}

pub fn format_phone_numer(numbers: &[u32]) -> Result<String, Error> {
    if numbers.len() != 10 {
        Err(Error::InvalidLength)
    } else if numbers.iter().any(|x| *x > 9) {
        Err(Error::NotSingleDigitInput)
    } else {
        Ok(format!(
            "({}{}{}) {}{}{}-{}{}{}{}",
            numbers[0],
            numbers[1],
            numbers[2],
            numbers[3],
            numbers[4],
            numbers[5],
            numbers[6],
            numbers[7],
            numbers[8],
            numbers[9],
        ))
    }
}

#[cfg(test)]
mod tests {
    use crate::*;

    #[test]
    fn it_for_a_valid_phone_number() {
        assert_eq!(
            format_phone_numer(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]),
            Ok("[phone]".to_string())
        );
        assert_eq!(
            format_phone_numer(&[3, 2, 1, 5, 5, 5, 3, 1, 6, 3]),
            Ok("[phone]".to_string())
        );
    }

    #[test]
    fn it_errors_invalid_length_phone_number() {
        assert_eq!(
            format_phone_numer(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 5, 6, 3]),
            Err(Error::InvalidLength)
        );
        assert_eq!(
            format_phone_numer(&[1, 2, 3, 4, 5, 6, 7,]),
            Err(Error::InvalidLength)
        );
    }

    #[test]
    fn it_errors_for_non_single_digit_numbers() {
        assert_eq!(
            format_phone_numer(&[10, 2, 3, 4, 5, 6, 7, 8, 9, 0]),
            Err(Error::NotSingleDigitInput)
        );
    }
}

[Franco Traversaro]

No PHP solutions yet? Here I come!

<?php

function phoneFormat(array $numbers): string
{
    if (10 !== count($numbers)) {
        throw new \RuntimeException("Wrong input");
    }
    array_unshift($numbers, '(%d%d%d) %d%d%d-%d%d%d%d');

    return call_user_func_array('sprintf', $numbers);
}

assert('[phone]' === phoneFormat([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]), "Function not functioning :-/");

But please edit the OP to explain what format do you want, not everybody comes from USA!

EDIT: added length validation

[Kasper Meyer]

Ruby solution

require "minitest/autorun"

class PhoneNumberFormatter
  def initialize digits
    @digits = digits
  end

  def format
    "(#{area_code}) #{central_office_code}-#{line_number}"
  end

  private

    def area_code
      @digits[0..2].join
    end

    def central_office_code
      @digits[3..5].join
    end

    def line_number
      @digits[6..9].join
    end
end

class PhoneNumberFormatterTest < MiniTest::Test
  def test_formatted_phone_number
    output = PhoneNumberFormatter.new([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]).format

    assert_equal "[phone]", output
  end
end

[Steve Moon]

Erlang: (in the REPL)

Num = [8,0,0,5,5,5,1,2,1,2].
io:format("(~B~B~B) ~B~B~B-~B~B~B~B~n", Num).
[phone]
ok

Or you can use io_lib:format and assign the result to a variable instead.

Checking for valid input is fairly trivial, but the Erlang convention is to assume that something this far into the system is okay, and correct for the error by dying and letting the supervisor deal with it.

[jmc]

Clojure:

(defn format-number [digits]
  (apply format "(%s%s%s) %s%s%s-%s%s%s%s" digits))

[Craig McIlwrath]

Haskell (US formatting):

formatNumber :: [Int] -> Maybe String
formatNumber xs
  | length xs /= 10 = Nothing
  | not $ and $ (map (<10) xs) ++ (map (>=0) xs) = Nothing 
  | otherwise = Just $ "(" ++ (showSlice 0 3 xs) ++ ") " ++ (showSlice 3 3 xs) ++ "-" ++ (showSlice 6 4 xs) 
  where showSlice from len = concat . map show . take len . drop from