union-find/contiguous

export default function rankedtreeunion(p, r, a, b) {
    if (r[a] < r[b]) {
        p[a] = b;
        return b;
    }

    if (r[a] > r[b]) {
        p[b] = a;
        return a;
    }

    p[b] = a;
    ++r[a];
    return a;
}