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CODE100 Puzzle: Thumbs up for the old school

The challenge was the following:

If 44-33-555-555-666 is hello and 9-666-777-555-3 is world, what is:


Can you do an encoder/decoder for this way of writing?

Solution explanation

What we are dealing with here is the way you texted on old feature phones. Each key represented several characters and you had to press them a few times to type a letter.

Old Mobile Device

So, to type a you would press 2 once, to type c you had to pressed 2 three times. To type o you pressed 6 three times and so on…

To convert the message here, the first thing to do is to define the keyset as an object:

const keycodes = {
    "0": " ", "2": "abc", "3": "def",
    "4": "ghi", "5": "jkl", "6": "mno",
    "7": "pqrs", "8": "tuv", "9": "wxyz"

Decoding the message works - for example in JavaScript - the following way:

const decode = message => {
    let result = [];
    message.split('-').forEach(item => {
    return result.join('');

That’s all there is to decode the message. Encoding a text into this format is a bit trickier.

const encode = text => {
    return text.split('').map(letter => {
        let str = '';
        Object.keys(keycodes).forEach(key => {
            if (keycodes[key].includes(letter)) {
                str = key.repeat(keycodes[key].indexOf(letter) + 1);
        return str;

ALl this would have the desired results:

// = we are developers
console.log(encode('sore thumbs'))
// = 7777-666-777-33-0-8-44-88-6-22-7777

We need a delimiter string like - in the code, as, for example 777777 would be ambiguous. Is it rr or qqq or ps?

Did you manage to do it? What was your solution? You can see other people’s submissions on the Gist.

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