Permutate / Combine

let permutate = (str, each) => {
    let now = str;
    const len = str.length;
    for (let n = 0; ; ) {
        each(now);
        ++ n;
        let a = len - 2;
        while (a >= 0 && now[a] >= now[a + 1]) --a;
        if (a < 0) {
            let s1 = '';
            for (let i=len; i; s1 += now[--i]);
            now = s1;
        } else {
            let b = len - 1;
            for (; now[b] <= now[a]; --b);
            let s1 = now.substring(0, a) + now[b];
            const s2 = now.substring(a + 1, b);
            const s3 = now.substring(b + 1, len);
            for (let i=s3.length; i; s1 += s3[--i]);
            s1 += now[a];
            for (let i=s2.length; i; s1 += s2[--i]);
            now = s1;
        }
        if (now === str) return n;
    }
};
let combine = (str, each) => {
    const idxMap = {};
    const chrArr = [];
    const maxArr = [];
    const max = str.length;
    for (let i=0; i<max; ++i) {
        const chr = str[i];
        let index = idxMap[chr];
        if (index === undefined) {
            idxMap[chr] = chrArr.length;
            chrArr.push(chr);
            maxArr.push(1);
        } else {
            ++ maxArr[index];
        }
    }
    const nChars = chrArr.length;
    const qtdArr = new Array(nChars).fill(0);
    for (let n = 0; ; ) {
        str = '';
        for (let i=0; i<nChars; ++i) {
            str += chrArr[i].repeat(qtdArr[i]);
        }
        each(str);
        ++ n;
        if (str.length === max) return n;
        for (let i=0; i<nChars && ++ qtdArr[i] > maxArr[i]; qtdArr[i++] = 0);
    }
};