Binary Search

Also known as half-interval search, logarithmic search, or binary chop.
A binary search is a search algorithm that can find the position of a value within a sorted array.
The function does not return the position, it just returns whether a match was found or not.
Your array must be sorted in Ascending Order for this function to work.

Public Sub BinarySearch() 
Dim myArray(0 To 3) As String
Dim bfoundMatch As String

    myArray(0) = "four"
    myArray(1) = "one"
    myArray(2) = "three"
    myArray(3) = "two"

    bfoundMatch = Array_Find(myArray, "three")
    Debug.Print bfoundMatch
End Sub

Public Function Array_Find(ByRef theArray() As String, _
                           ByVal target As String) _
                           As Boolean

Dim bfind As Boolean
Dim low As Integer
Dim high As Integer
Dim middle As Integer
    low = 0
    high = UBound(theArray)

    bfind = False
    Do While low <= high
        middle = (low + high) / 2

        If target = theArray(middle) Then
            bfind = True
            Exit Do

        ElseIf target < theArray(middle) Then
            high = (middle - 1)
            low = (middle + 1)
        End If
    Array_Find = bfind
End Function

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