Question

我需要编写一个函数来在VB.NET中查找字符串中的第一个非重复字符。下面的代码看起来不错吗？

Module Module2

Sub Main()
    ' Unit test
    ' Pass string as argument.
    Console.WriteLine(nonRepeat("BBEEXEE")

End Sub

Function nonRepeat(ByVal aString As String) As String

    Dim repeated As Integer = 0

    For i = 0 To aString.Length-1

        repeated = 0

        For j = 0 To aString.Length-1

            ' If inner and outer For loops are on the same index then
            ' inner For loop moves to next index and compares character 
            ' with outer For loop character.
            ' If characters are equal then set repeated = 1 and Exit inner For loop.
            ' Otherwise, continue to find repeating character
            ' If reached end of string without finding repeating character
            ' then non-repeating character has been found and is returned.

            If ((i <> j) AndAlso (aString(i) = aString(j))) Then

                ' Found repeating character 
                repeated = 1

                Exit For

            End If

        Next

        If (repeated = 0) Then

            ' Found first non-repeating character
            Return aString(i)

        End If
    Next

    Return ("No Non-Reapeating character!")

End Function

End Module

Answer 1

不，您的代码将抛出异常，因为您的循环将耗尽要处理的数据。你的循环需要以.Length -1结尾。否则，它应该工作。

但是，您可以提高效率并处理边缘情况：

    ' Don't bother checking if the string is empty
    If Not String.IsNullOrEmpty(asString) Then
        ' If the string is only a single character, just return it
        If asString.Length = 1 Then
            Return asString
        End If

        ' Create a collection that records the number of occurences for each character
        Dim cCharacterCounts As New System.Collections.Generic.Dictionary(Of Char, Integer)

        For Each cCharacter As Char In asString
            If cCharacterCounts.ContainsKey(cCharacter) Then
                ' If the character exists, increment its count
                cCharacterCounts(cCharacter) += 1
            Else
                ' Otherwise record the character as a new entry, initializing the count to 1
                cCharacterCounts.Add(cCharacter, 1)
            End If
        Next

        ' Now find the first character which only has a single count. This will be the first non-repeating value.
        For Each cCharacter As Char In cCharacterCounts.Keys
            If cCharacterCounts(cCharacter) > 1 Then
                Return cCharacter.ToString()
            End If
        Next
    End If

    ' Handle the case in which there is no non-repeating character
    Return String.Empty

Answer 2

一点linq可以缩短它。

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
    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
End Module

Answer 3

Dim str As String = "BBEEXEE"
    For Each ch As Char In str
        If str.Contains(ch & ch) = False Then
            'first non-repeating
            MsgBox("First non-repeating character is: " & ch)
            Exit For
        End If
    Next

在VB.NET中查找字符串中的第一个非重复字符

3 个答案: