Fastest way to detect duplicate numbers on array vb.net 2005

Question

I have this project that let user inputs 5 different numbers from 1 to 50. But I want to validate it before saving to DB that i will be 5 unique numbers. What\'s the best an

Answer 1

Pseudocode:

integer numbers[50]
zeroarray(numbers, 50)

integer count = 0;
while (count < 5)
{
   integer value = getinput()

   if (value >= 1 and value <= 50)
     if (numbers[value] = 0)
     {
        count = count + 1
        numbers[value] = 1
     }
     else
        reject duplicate
   else
     reject invalid
}

Answer 2

Reed Copsey's suggestion to use hash sets was a good one (I hadn't worked with the HashSet class before).

But I then discovered that the IEnumerable class offers an extension method called Distinct that copies the unique values from a source IEnumerable to a target IEnumerable.

Borrowing the first line of Reed's sample code, here's the new sample VB.NET code:

    Dim numbers As IEnumerable(Of Integer) = GetInputFromUser()
    Dim isUnique As Boolean = (numbers.Distinct.Count = numbers.Count)

The variable isUnique is True if the numbers IEnumerable contains no duplicate values, or False if it contains one or more duplicate values.

Answer 3

Put in an array, sort it and check if elements 1,2 2,3 3,4 and 4,5 are different (in a loop).

Answer 4

To simplifiy lets say the user inputs 5 different numbers from 0 to 49.

You can create a Boolean Array IsUsed(49) with 50 elements.

Then when the user input the value iInputNum=30 you can set IsUsed(30)=TRUE. Next time, when the user input the second value iInputNum=7, you can set IsUsed(7)=TRUE In this way you can check in a very fast way if the number was already inserted.

if IsUsed(iInputNum) then
   'Skip the Input (put the right code here)
else
   'Accept the number
   IsUsed(iInputNum)=TRUE
   'save iInputNum in the database
end if

Do not forget to clear the array after inserting all 5 numbers. Remenber to put the right index in order to handle the number 1-50 (e not 0-49)

Answer 5

You can try this very simple method: Filtering Arrays using LINQ

Answer 6

Check this code

Private Function HasDuplicates(ByVal arr As Array) As Boolean
    For i As Integer = 0 To arr.Length - 1
        If Not arr(i) Is Nothing Then
            Dim l As Integer = Array.LastIndexOf(arr, arr(i))
            If l <> i Then Return True
        End If
    Next
    Return False
End Function