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This challenge was given to WeAreDevelopers by our partners Twilio.

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SMS messages can be encoded in different character encodings to optimize space. The two main types of encodings are:

When an SMS message contains characters outside the GSM-7 character set, it must be encoded in UCS-2. This significantly reduces the number of characters that can fit into a single SMS segment.

Don’t worry, when using Twilio Programmable Messaging, this will be done automatically for you :)


Create a function that determines whether an SMS message body can be encoded using GSM-7 or if it requires UCS-2 encoding. The function should also calculate the length of the message in bits for the required encoding.

Write a function that, given a text string representing the body of an SMS, determines:

  1. Whether the message can be encoded using GSM-7 or if it requires UCS-2 encoding.
  2. The length of the message in bits.



Example Input / Output

These tests are available in the dataset.json file to use to create your function.

Helpful Background Knowledge


Solution in JS

function determineEncodingAndLength(message) {
    const gsm7Characters = '@£$¥èéùìòÇ\nØø\rÅåΔ_ΦΓΛΩΠΨΣΘΞ\x1bÆæßÉ' +
          ' !"#$%&\'()*+,-./0123456789:;<=>?¡ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÑÜ`' +
    function isGSM7Character(char) {
        return gsm7Characters.indexOf(char) !== -1;
    let isGSM7 = true;
    for (let i = 0; i < message.length; i++) {
        if (!isGSM7Character(message[i])) {
            isGSM7 = false;
    const encoding = isGSM7 ? 'GSM-7' : 'UCS-2';
    const lengthInBits = isGSM7 ? message.length * 7 : message.length * 16;
    return [encoding, lengthInBits];
// Test messages
const messages = [
    "Ahoy World",
    "This is a test message with special characters: ñáéíóú.",
    "Visit the Twilio booth at Hall A 03 during WeAreDeveloper World Congress",
    "Rumors say Twilio will provide healthy smoothies 🥤🍓🍍",
messages.forEach(msg => {
    const [encoding, messageLength] = determineEncodingAndLength(msg);
    console.log(`Message: ${msg}`);
    console.log(`Encoding: ${encoding}`);
    console.log(`Length: ${messageLength}`);

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