Sort an array alphabetically and return a number representation for every character

Question

I want to try to make my own function. I want to sort an array of characters in increasing order and return the occurrence count of each character as a compact number.

Example:

function numberRepresentation(arr) {
    // arr is an array
    // return a number

    /*
    ex. arr=[b,a,a,a,c,b,a]
    after sorting array will look like arr=[a,a,a,a,b,b,c]
    occurrence of characters -> a = 4, b = 2, c = 1 
    so output will be 421
    */
}

How can I do it?

Answer 1

function numberRepresentation(arr) {
    return arr.reduce((counts, letter) => {
        const code = letter.charCodeAt(0)
        counts[code] = counts[code] + 1 || 1
        return counts
    }, []).join('')
}

Explanation:

We just count occurrence of every letter, but we use a simple Array and char codes as indexes. Thus we automatically get a list of counts of letters ordered alphabetically (because the char codes go in abc order). So all we need to do is concatenate all the counts and return.