Excel VBA Highlight Cells Based on Same Groups from Different Column

I have a large data set in which Column A specifies a Group name and column D specifies a number that needs to be unique PER group.

I'd like to use VBA to highlight any Duplicate cells in Column D, for same Groups from Column A.

Ex:

In this case, cells for Group 1 containing "20" would be highlighted and cells for Group 2 containing "33" would be highlighted.

Modifying my linked post:

Sub HiliteDups()
    Const HILITE_COLOR = vbRed
    Dim ws As Worksheet, k
    Dim dict As Object, rng As Range, data, r As Long
     
    'Set dict = CreateObject("scripting.dictionary") 'Windows
    Set dict = New Dictionary                        'Cross-platform
    '   (https://github.com/VBA-tools/VBA-Dictionary)
    
    Set ws = ActiveSheet 'for example
    Set rng = ws.Range("A2:D" & ws.Cells(Rows.Count, "A").End(xlUp).Row)
    rng.Columns(4).Interior.ColorIndex = xlNone 'clear flags
    data = rng.Value  'get data as array (for faster looping)
    
    For r = 1 To UBound(data, 1)           'loop over range data
        k = data(r, 1) & "<>" & data(r, 4) 'composite key A+D
        If dict.Exists(k) Then
            If dict(k) > 0 Then 'need to color the first row for this key?
                rng.Cells(dict(k), 4).Interior.Color = HILITE_COLOR
                dict(k) = 0
            End If
            rng.Cells(r, 4).Interior.Color = HILITE_COLOR 'color this row
        Else
            dict.Add k, r 'remember this row in case there are duplicates later
        End If
    Next r
End Sub

EDIT - allow for use of cross-platform dictionary class from:
https://github.com/VBA-tools/VBA-Dictionary

And another alternative: using a Collection with keys

Sub HiliteDups()
    Const HILITE_COLOR = vbRed
    Dim ws As Worksheet, k As String, valA, valD
    Dim col As Collection, rng As Range, data, r As Long, v
     
    Set ws = ActiveSheet 'for example
    Set rng = ws.Range("A2:D" & ws.Cells(Rows.Count, "A").End(xlUp).Row)
    rng.Columns(4).Interior.ColorIndex = xlNone 'clear flags
    data = rng.Value  'get data as array (for faster looping)
    
    Set col = New Collection 'for tracking unique A+D combinations
    For r = 1 To UBound(data, 1)           'loop over range data
        valA = data(r, 1)
        valD = data(r, 4)
        If Len(valA)>0 And Len(valD)>0 Then
            k = valA & "<>" & valD 'composite key A+D
            v = KeyValue(col, k)
            If Not IsEmpty(v) Then
                If v > 0 Then 'need to color the first row for this key?
                    rng.Cells(v, 4).Interior.Color = HILITE_COLOR
                    col.Remove k 'remove keyed value
                    col.Add 0, k 're-add as zero
                End If
                rng.Cells(r, 4).Interior.Color = HILITE_COLOR 'color this row
            Else
                col.Add Item:=r, Key:=k 'remember this row and key in case there are duplicates later
            End If  'key was found?
        End If      'values in A and D?
    Next r
End Sub

'Retrieve value for key `k` from collection `col`
'  Returns Empty if there's no such key
Function KeyValue(col As Collection, k As String)
    On Error Resume Next 'ignore error if no match for `k`
    KeyValue = col.Item(k)
End Function