Imports System
Public Class Program
Public Shared Function findElementThatAppearsOnce(ByVal arr As Integer()) As Integer
Dim size As Integer = arr.Length
Dim element As Integer = arr(0)
For i As Integer = 1 To size - 1
element = element Xor arr(i)
Next
Return element
End Function
Public Shared Sub Main()
Dim arr As Integer() = {7, 2, 2, 4, 5, 3, 4, 5, 7}
Console.Write(findElementThatAppearsOnce(arr))
End Sub
End Class
' run
'
' 3
'