Imports System
Imports System.Collections.Generic
Imports System.Linq
Module UniqueRandomIndices
'---------------------------------------------------------------
' Select N unique random indices from an existing array.
'
' Approach:
' - Build a list of indices: 0, 1, 2, ..., size-1.
' - Shuffle the list using Random + OrderBy.
' - Take the first N shuffled indices — guaranteed unique.
' - Return those indices to the caller.
'---------------------------------------------------------------
Function PickUniqueIndices(arraySize As Integer, count As Integer) As List(Of Integer)
If count > arraySize Then
Throw New ArgumentException("Cannot pick more unique indices than array size.")
End If
' Build index list
Dim indices As New List(Of Integer)(arraySize)
For i As Integer = 0 To arraySize - 1
indices.Add(i)
Next
' Shuffle indices
Dim rng As New Random()
indices = indices.OrderBy(Function(x) rng.Next()).ToList()
' Return first N indices
Return indices.Take(count).ToList()
End Function
Sub Main()
' Example array
Dim data() As Integer = {5, 12, 5, 19, 5, 33, 47, 5, 58, 61, 17, 3, 5, 74, 83, 90, 6}
Dim N As Integer = 6 ' number of unique indices to pick
' Get unique random indices
Dim indices As List(Of Integer) = PickUniqueIndices(data.Length, N)
' Print results
Console.WriteLine("Random unique indices and their values:")
For Each idx In indices
Console.WriteLine("index " & idx & " -> value " & data(idx))
Next
End Sub
End Module
' run:
'
' Random unique indices and their values:
' index 5 -> value 33
' index 10 -> value 17
' index 6 -> value 47
' index 2 -> value 5
' index 1 -> value 12
' index 12 -> value 5
'
