BinarySearch List

BinarySearch is an optimized search Function. It requires that the List instance is already sorted. It provides better performance on sorted Lists.

This method hones in on the value by dividing the number of elements being searched several times. It can speed up searches in some real-world programs.

An example

This example program adds 3 Strings to the List instance. The List is then sorted with the Sort Function. It is important to Sort here.

Module Module1
    Sub Main()
        Dim animals As List(Of String) = New List(Of String)
        animals.Add("zebra")
        animals.Add("mouse")
        animals.Add("cat")

        ' This is required!
        animals.Sort()

        Dim zebraPosition As Integer = animals.BinarySearch("zebra")
        Dim catPosition As Integer = animals.BinarySearch("cat")

        Console.WriteLine(zebraPosition)
        Console.WriteLine(catPosition)
    End Sub

End Module
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Performance

In many programs, it is better to use Dictionary for lookups. The hashing mechanism in a Dictionary provides good performance for many real-world programs.

Performance, IndexOf

BinarySearch is faster than IndexOf on large sorted Lists. But sometimes we know where an element may occur—we can then use IndexOf to reduce searching time.

There is an important use case for BinarySearch. If performance is critical, a hashed lookup is often superior. And if elements are not sorted, IndexOf is required.