AAABBACDDDAFFEEEELL => A3B2ACD3AF2E4L

/*
    Разложить множество на подмножетсва (AAABBACDDDAFFEEEELL => A3B2ACD3AF2E4L2)
*/


const mn = 'AAABBACDDDAFFEEEELL';

function minimalize(str) {
    let stack = [str[0]];
    let count = 0;
    let result = '';

    for (let i = 0; i <= str.length; i++) {
        let c = str[i];

        if (stack[0] === c) {
            count++;
        } else {
            result += stack.pop() + (count !== 1 ? count : '');
            stack.push(c);
            count = 1;
        }
    }

    return result;
}