CODE EXAMPLE FOR JAVASCRIPT

shrinkStringByRepeatFactor

const howMany = (str) => str

    .toLowerCase()
    .split("")
    .sort()
    .join("")
    .match(/(.)1+/g)


const repet = (str, num) => {
    const filter = howMany(str)
    let result = ''
    for (let i = 0; i < filter.length; i++) {
        if (filter[i].length === num) {
            result += filter[i].charAt(0)
        }
    }

    return result
}