Regex javascript to vb

Question

I have a javascript function maxRepeat. Im having trouble translating it to vb.net, seems regex engine differs...and Im not so strong on regex. Would you mind pointing me in the right direction for translating the regex string to the appropriate vb.net one ? ...I understand how to do the logic afterwords, just lost on the regex string...

Im talking about this function..

function maxRepeat(input) {
        var reg = /(?=((.+)(?:.*?\2)+))/g;
        var sub = ""; 
        var maxstr = ""; 
        reg.lastIndex = 0; 
        sub = reg.exec(input); 
        while (!(sub == null)) {
            if ((!(sub == null)) && (sub[2].length > maxstr.length)) {
                maxstr = sub[2];
            }
            sub = reg.exec(input);
            reg.lastIndex++; 
        }
        return maxstr;
    }

This functions returns the largest sequence of characters that appear at least twice. "one two one three one four" would return "one t" <--with space || "onetwoonethreeonefour" would return "onet"

"324234241122332211345435311223322112342345541122332211234234324" returns "1122332211234234"

Wiktor Stribiżew · Accepted Answer · 2015-04-09 00:15:33Z

First, SO "is not a converting service", but I got curious myself. Second, your regex is totally fine for use in VB.NET. Third, you can leverage Regex.Matches rather than checking matches sequentially. And lastly, you cannot name a variable 'sub', it is a reserved word in VB.NET.

Now, this is your function in VB.NET:

Private Function maxRepeat(input As String) As String
   maxRepeat = String.Empty
   Dim reg As String = "(?=((.+)(?:.*?\2)+))"
   For Each m As Match In Regex.Matches(input, reg)
      If m IsNot Nothing And m.Groups(2).Value.Length > maxRepeat.Length Then
           maxRepeat = m.Groups(2).Value
      End If
   Next
End Function

Or, with LINQ (do not forget System.Linq reference):

Private Function maxRepeat(input As String) As String
    maxRepeat = String.Empty
    Dim reg As String = "(?=((.+)(?:.*?\2)+))"
    Dim matches As IEnumerable(Of Match) = Regex.Matches(input, reg).Cast(Of Match)().Select(Function(m) m)
    maxRepeat = (From match In matches
                Let max_val = matches.Max(Function(n) n.Groups(2).Value.Length)
                Where match.Groups(2).Value.Length = max_val
                Select match.Groups(2).Value).FirstOrDefault()
End Function

The function may be called the following way:

Dim res As String = maxRepeat("324234241122332211345435311223322112342345541122332211234234324")

Result:

1122332211234234

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