Simple disjoint set which I don't know if it works or not.

disjoint_set.cpp

// from https://github.com/spakin/disjoint
class disjoint_set {
private:
    typedef struct {
        int rank;
        int parent;
    } element;
    vector<element> set_list;
public:
    explicit disjoint_set(int size) {
        set_list.resize(size);
        for (int i = 0; i < size; i++)
            set_list[i].parent = i;
    }

    int find(int e) {
        while (set_list[e].parent != e) {
            set_list[e].parent = set_list[set_list[e].parent].parent;
            e = set_list[e].parent;
        }
        return e;
    }

    void union_set(int e1, int e2) {
        int e1Root = find(e1);
        int e2Root = find(e2);
        if (e1Root == e2Root)
            return;

        if (set_list[e1].rank < set_list[e2].rank)
            set_list[e1].parent = e2;
        else if (set_list[e1].rank > set_list[e2].rank)
            set_list[e2].parent = e1;
        else {
            set_list[e2].parent = e1;
            set_list[e1].rank++;
        }
    }
};