union-find/non-contiguous

export default function rankedtreeunion(a, b) {
    if (a.rank < b.rank) {
        a.parent = b;
        return b;
    }

    if (a.rank > b.rank) {
        b.parent = a;
        return a;
    }

    b.parent = a;
    ++a.rank;
    return a;
}