CODE100 Puzzle: Thumbs up for the old school

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.

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 => {
        result.push(keycodes[item[0]][item.length-1]);
    })
    return result.join('');
};

• You define an array called result.
• You split the message into chunks at the - and loop over them
• This gives you strings like 9, 33, 0, 2, 777…
• You take the first letter of each of those strings (item[0]) and use it as they key of the object keycodes. You use the length of each item to get the right entry in the keyset.
• So, if the string is 777, we get the keyset[7], which is pqrs and the third item, which is r.
• You add that as a new item to the array result.
• Once all the chunks are done, you join the result array back into a string.

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;
    }).join('-');
};

• You take the text and split it into single letters.
• You start a new, empty string called str
• You loop over all the keys of the keycode object and check if their value includes the letter.
• If it does, you detect where in the value the letter is using indexOf and repeat the key value that amount of time.
• So if the letter is r, you detect that it is in the object property 7 as the third letter, which makes str the value of 777. Or w would be in the 9 property as the first value, which makes str also 9.
• You return str to override the original chunk of the array that resulted in the split.
• Once all letters are done, you join the splitted array back into a string with a - delimiter.

ALl this would have the desired results:

console.log(decode('9-33-0-2-777-33-0-3-33-888-33-555-666-7-33-777-7777'))
// = 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.