How to VBA code to count duplicates FAST

Requirement:

The user has a macro that loops through thousands of cells and creates a long list of item numbers (see attached file, column A).

Once the list is created (as a preparation for the next steps in the code), the user needs to count how many times each item appears. To be more specific, the user needs to know the sequential number of the appearance (#1, #2, #3, etc.) (See attached file, column B).

The best way the user has found to achieve that, is by using the countif function, which the code embeds in the file (later on, the code copy-paste the entire column as values).

The thing is, these formulas take a lot of time to calculate.

My questions is: Is there another way (perhaps an array formula) to get the “counting” added next to each item number (replacing this countif formula), which will work much faster?

https://www.ozgrid.com/forum/forum/help-forums/excel-vba-macros/147495-vba-code-to-count-duplicates-fast

Solution:

This uses a dictionary

Code:

Sub countThings()
    Dim ws As Worksheet
    Dim lastRow As Long, x As Long
    Dim items As Object
    
    Application.ScreenUpdating = False
    
    Set ws = Sheet1
    
    lastRow = ws.Range("A" & Rows.Count).End(xlUp).Row
    
    Set items = CreateObject("Scripting.Dictionary")
    For x = 1 To lastRow
        If Not items.exists(ws.Range("A" & x).Value) Then
            items.Add ws.Range("A" & x).Value, 1
            ws.Range("C" & x).Value = items(ws.Range("A" & x).Value)
        Else
            items(ws.Range("A" & x).Value) = items(ws.Range("A" & x).Value) + 1
            ws.Range("C" & x).Value = items(ws.Range("A" & x).Value)
        End If
    Next x
    
    
End Sub

Obtained from the OzGrid Help Forum.

Solution provided by bryce.