One of the best ways to get to know a programmer is to see their code. You might not know their favorite hobbies, favorite foods, or favorite football team (trick question, programmers don’t like football. Hehe), but getting a glimpse at how someone goes about solving problems can really be quite helpful.
With that in mind, I’m going to be taking part in ProjectEuler.net. It’s all math-based to one degree or another. I am horrible at math, really. I know enough to get by, but a lot of it I’ve forgotten since being out of school. But, I must admit, I love a figuring out puzzles — especially by programming — so I’m anxious to get started.
If you’d like to follow along, feel free to set up an account on their site and try the stuff out yourself. It can get quite addictive :)
Since I’m going to post code-samples here, I might as well include one of my “helper” routines I ended up using in a couple of solutions. Since a few of the problems involved prime numbers, I made a generic function for allowing me to determine whether a specific number is a prime or not.
I’m sure there are more effective ways of figuring out if a number is a prime, but math was never a subject a particularly excelled at…
Function IsPrime(ByVal tmpVal As Long) As Boolean
Dim strVal As String = tmpVal.ToString
'If the number ends in 0,2,4,5,6,8 then it's NOT prime (might be a composite)
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "0" Then Return False
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "2" Then Return False
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "4" Then Return False
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "5" Then Return False
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "6" Then Return False
If strVal.Length > 1 AndAlso strVal.Substring(strVal.Length - 1, 1) = "8" Then Return False
'Except for the number 2, if a number is even, it's always composite
If tmpVal <> 2 AndAlso tmpVal Mod 2 = 0 Then Return False
'If a number's digits add up to a number which is divisible by 3, it's composite
Dim tmpDigitSum As Integer = 0
If strVal.Length > 1 Then
For k As Integer = 0 To strVal.Length - 1
tmpDigitSum += strVal.Substring(k, 1)
Next
If tmpDigitSum = 3 Then Return False
End If
'If a number's square root is an integer, it's a composite
If System.Math.Sqrt(tmpVal) = CInt(System.Math.Sqrt(tmpVal)) Then Return False
'If it's not divisible by itself, it's not Prime
If tmpVal Mod tmpVal <> 0 Then Return False
Dim MaxVal As Long = System.Math.Sqrt(tmpVal)
For k As Long = 2 To MaxVal
If tmpVal Mod k = 0 AndAlso k <> 1 Then
Return False
End If
Next
Return True
End Function