Introduction

Like I said in a previous post of mine.

From time to time I answer a few questions on Stackoverflow, mostly because you can learn a lot from someone else’s problems and it makes you think.

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Thinking is something you need to practice every day.

This time the problem was simple and it seems like most people revert to a for loop loop to solve it. While using linq is so much shorter easier to read.

The question

The question was how to “Find the first non-repeating character in a string in VB.NET”

First of all we need some more test data.

Imports System.Linq

Module Module1

    Sub Main()
        Console.WriteLine(FirstCharacterToNotRepeat(Nothing))
        Console.WriteLine(FirstCharacterToNotRepeat(""))
        Console.WriteLine(FirstCharacterToNotRepeat("BBEEXEE"))
        Console.WriteLine(FirstCharacterToNotRepeat("BBEEEE"))
        Console.WriteLine(FirstCharacterToNotRepeat("XBBEEEE"))
        Console.WriteLine(FirstCharacterToNotRepeat("BBEEEEX"))
        Console.WriteLine(FirstCharacterToNotRepeat("BBEEXEEACEED"))
        Console.ReadLine()
    End Sub

    Private Function FirstCharacterToNotRepeat(ByVal input As String) As String
        return String.Empty
    End Function
End Module

And now we need some answers.

The for loop

Here is my solution using a for loop.

vbnet Private Function FirstCharacterToNotRepeat(ByVal input As String) As String If String.IsNullOrEmpty(input) Then Return String.Empty Dim charlist As New Dictionary(Of Char, Int32) For Each c In input If charlist.Keys.Contains(c) Then charlist(c) = charlist(c) + 1 Else charlist.Add(c, 1) End If Next For Each c In charlist If c.Value = 1 Then Return c.Key Next Return String.Empty End Function There are actually 2 for loops in there, one to put every character in the dictionary and count the occurrences and one to get out the first element that has only 1 occurrence.

The linq solution

And here is my linq solution.

vbnet Private Function FirstCharacterToNotRepeat(ByVal input As String) As String If String.IsNullOrEmpty(input) Then Return String.Empty Return (input.GroupBy(Function(x) x).Where(Function(x) x.Count = 1).Select(Function(x) x.First))(0) End Function First I do a group by on all characters. Then I do a where on the count of the result of the group by, where I only want the occurrences with a count of 1. And then I just select the first occurrence with a count of 1.

Simple.

Conclusion

Knowing and using linq can make your code so much shorter and easier for you to write and read.