Task: Set consolidation
C++: #include <algorithm>
#include <iostream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;


void SimpleConsolidate(vector<unordered_set<char>>& sets)
{
    
    for(auto last = sets.rbegin(); last != sets.rend(); ++last)
        for(auto other = last + 1; other != sets.rend(); ++other)
        {
            bool hasIntersection = any_of(last->begin(), last->end(), 
                                          [&](auto val)
                                          { return other->contains(val); });
            if(hasIntersection)
            {
                other->merge(*last);
                sets.pop_back();
                break;
            }
        }
}



struct Node
{
    char Value;
    Node* Parent = nullptr;
};    

Node* FindTop(Node& node)
{
    auto top = &node;
    while (top != top->Parent) top = top->Parent;
    for(auto element = &node; element->Parent != top; )
    {
        
        auto parent = element->Parent;
        element->Parent = top;
        element = parent;
    }
    return top;
}

vector<unordered_set<char>> FastConsolidate(const vector<unordered_set<char>>& sets)
{
    unordered_map<char, Node> elements;
    for(auto& set : sets)
    {
        Node* top = nullptr;
        for(auto val : set)
        {
            auto itr = elements.find(val);
            if(itr == elements.end())
            {
                
                auto& ref = elements[val] = Node{val, nullptr};
                if(!top) top = &ref;
                ref.Parent = top;
            }
            else
            {
                auto newTop = FindTop(itr->second);
                if(top)
                {
                    top->Parent = newTop;
                    itr->second.Parent = newTop;
                }
                else
                {
                    top = newTop;
                }
            }
        }
    } 

    unordered_map<char, unordered_set<char>> groupedByTop;
    for(auto& e : elements)
    {
        auto& element = e.second;
        groupedByTop[FindTop(element)->Value].insert(element.Value);
    }

    vector<unordered_set<char>> ret;
    for(auto& itr : groupedByTop)
    {
        ret.push_back(move(itr.second));
    }

    return ret;
}

void PrintSets(const vector<unordered_set<char>>& sets)
{
    for(const auto& set : sets)
    {
        cout << "{ ";
        for(auto value : set){cout << value << " ";}
        cout << "} "; 
    }
    cout << "\n";
}

int main()
{
    const unordered_set<char> AB{'A', 'B'}, CD{'C', 'D'}, DB{'D', 'B'}, 
                              HIJ{'H', 'I', 'K'}, FGH{'F', 'G', 'H'};
                              
    vector <unordered_set<char>> AB_CD {AB, CD};
    vector <unordered_set<char>> AB_DB {AB, DB};
    vector <unordered_set<char>> AB_CD_DB {AB, CD, DB};
    vector <unordered_set<char>> HIJ_AB_CD_DB_FGH {HIJ, AB, CD, DB, FGH};

    PrintSets(FastConsolidate(AB_CD));
    PrintSets(FastConsolidate(AB_DB));
    PrintSets(FastConsolidate(AB_CD_DB));
    PrintSets(FastConsolidate(HIJ_AB_CD_DB_FGH));

    SimpleConsolidate(AB_CD);
    SimpleConsolidate(AB_DB);
    SimpleConsolidate(AB_CD_DB);
    SimpleConsolidate(HIJ_AB_CD_DB_FGH);

    PrintSets(AB_CD);
    PrintSets(AB_DB);
    PrintSets(AB_CD_DB);
    PrintSets(HIJ_AB_CD_DB_FGH);
}

VB: Private Function has_intersection(set1 As Collection, set2 As Collection) As Boolean
    For Each element In set1
        On Error Resume Next
        tmp = set2(element)
        If tmp = element Then
            has_intersection = True
            Exit Function
        End If
    Next element
End Function
Private Sub union(set1 As Collection, set2 As Collection)
    For Each element In set2
        On Error Resume Next
        tmp = set1(element)
        If tmp <> element Then
            set1.Add element, element
        End If
    Next element
End Sub
Private Function consolidate(sets As Collection) As Collection
    For i = sets.Count To 1 Step -1
        For j = sets.Count To i + 1 Step -1
            If has_intersection(sets(i), sets(j)) Then
                union sets(i), sets(j)
                sets.Remove j
            End If
        Next j
    Next i
    Set consolidate = sets
End Function
Private Function mc(s As Variant) As Collection
    Dim res As New Collection
    For i = 1 To Len(s)
        res.Add Mid(s, i, 1), Mid(s, i, 1)
    Next i
    Set mc = res
End Function
Private Function ms(t As Variant) As Collection
    Dim res As New Collection
    Dim element As Collection
    For i = LBound(t) To UBound(t)
        Set element = t(i)
        res.Add t(i)
    Next i
    Set ms = res
End Function
Private Sub show(x As Collection)
    Dim t() As String
    Dim u() As String
    ReDim t(1 To x.Count)
    For i = 1 To x.Count
        ReDim u(1 To x(i).Count)
        For j = 1 To x(i).Count
            u(j) = x(i)(j)
        Next j
        t(i) = "{" & Join(u, ", ") & "}"
    Next i
    Debug.Print "{" & Join(t, ", ") & "}"
End Sub
Public Sub main()
    show consolidate(ms(Array(mc("AB"), mc("CD"))))
    show consolidate(ms(Array(mc("AB"), mc("BD"))))
    show consolidate(ms(Array(mc("AB"), mc("CD"), mc("DB"))))
    show consolidate(ms(Array(mc("HIK"), mc("AB"), mc("CD"), mc("DB"), mc("FGH"))))
End Sub