【VBA】重複データを高速に取得する方法

Option Explicit
Sub FindDuplicateData()
    Dim ws As Worksheet
    Set ws = ThisWorkbook.Sheets("Sheet1")
    Application.ScreenUpdating = False
    
    ' 最終行の取得
    Dim lastRow As Long
    lastRow = ws.Cells(ws.Rows.Count, "A").End(xlUp).Row
    
    ' 重複データを格納する配列
    Dim duplicates() As Variant
    ReDim duplicates(1 To lastRow)
    
    ' 重複チェック用のコレクション
    Dim dict As Object
    Set dict = CreateObject("Scripting.Dictionary")
    
    ' データを走査
    Dim i As Long, j As Long
    For i = 1 To lastRow
        If Not dict.exists(ws.Cells(i, "A").Value) Then
            dict.Add ws.Cells(i, "A").Value, i
        Else
            ' 重複データを配列に格納
            duplicates(dict(ws.Cells(i, "A").Value)) = ws.Cells(i, "A").Value
            duplicates(i) = ws.Cells(i, "A").Value
        End If
    Next i
    
    ' 結果の表示
    Dim resultRow As Long
    resultRow = lastRow + 1
    For j = LBound(duplicates) To UBound(duplicates)
        If duplicates(j) <> Empty Then ws.Cells(resultRow, "B").Value = duplicates(j): resultRow = resultRow + 1
    Next j
    
    Application.ScreenUpdating = True
End Sub