function lev(a, b) {
    if (!a.length) return b.length;
    if (!b.length) return a.length;
    const arr = [];
    for (let i = 0; i <= b.length; i++) {
        arr[i] = [i];
        for (let j = 1; j <= a.length; j++) {
            arr[i][j] = i === 0 ?
                j : Math.min(
                    arr[i - 1][j] + 1,
                    arr[i][j - 1] + 1,
                    arr[i - 1][j - 1] + (a[j - 1] === b[i - 1] ? 0 : 1)
                );
        }
    }
    return arr[b.length][a.length];
};