Imports System
Public Class Program
Friend Shared Sub count_odd_and_even_sum_of_pairs(ByVal arr As Integer(), ByVal evenodd As Integer())
Dim total_even As Integer = 0, total_odd As Integer = 0
Dim size As Integer = arr.Length
For i As Integer = 0 To size - 1
If arr(i) Mod 2 = 0 Then
total_even += 1
Else
total_odd += 1
End If
Next
' For all the even elements -> sum of the pair will be even
Dim evenPairs As Integer = ((total_even * (total_even - 1)) / 2)
' For all the odd elements -> sum of the pair will be even
evenPairs += ((total_odd * (total_odd - 1)) / 2)
' All even elements * all odd element -> sum of the pair will be odd
Dim oddPairs As Integer = total_even * total_odd
evenodd(0) = evenPairs
evenodd(1) = oddPairs
End Sub
Public Shared Sub Main(ByVal args As String())
Dim arr As Integer() = New Integer() {1, 2, 3, 4, 5}
Dim evenodd As Integer() = New Integer(1) {}
' 1 + 3, 1 + 5, 2 + 4, 3 + 5 = 4 Even
' 1 + 2, 1 + 4, 2 + 3, 2 + 5, 3 + 4, 4 + 5 = 6 Odd
count_odd_and_even_sum_of_pairs(arr, evenodd)
Console.WriteLine("Total Even Sum = " & evenodd(0))
Console.WriteLine("Total Odd Sum = " & evenodd(1))
End Sub
End Class
' run:
'
' Total Even Sum = 4
' Total Odd Sum = 6
'
