Kruskal's algorithm (MST)

struct vertex
{
    int parent, size;
};

struct edge
{
    int from, to, weight;
};

std::vector<edge> Kruskal(std::vector<std::vector<edge>>& edges)
{
    std::vector<edge> min_tree;

    // If there are no edges, return a null-tree
    if (edges.size() < 2)
        return min_tree;

    // Sort the edges by increasing weight
    std::sort(edges.begin(), edges.end(), [](edge& l, edge& r) -> bool {
            return l.weight < r.weight;
        });

    // Keep adding edges that merge merge connected components until there is one connected component left
    for (edge& e : edges)
        if (ds_union(e.from, e.to))
        {
            min_tree.push_back(e);
            if (min_tree.size() == vertices.size() - 1)
                return min_tree;
        }

    // If this point has been reached, the original graph isn't connected
    return min_tree;
}