function serializeString(input) {

    let indexes = [];

    for (let i = 0; i < input.length; i++) {
        let currentLetter = input[i];

        for (let j = 0; j < input.length; j++) {
            if (currentLetter === input[j]) {
                indexes.push(j)
            }
        }

        console.log(`${currentLetter}:${indexes.join('/')}`);
        indexes = [];
    }
}