Pythagorean triples

[corwood]

I am in a VB .NET class, and one of the assignments is to use loops to generate a list of all the pythagorean triples where legA and legB <100 and hypotenuse < 200, and then put this list into a listbox.
I have done this so far:

 'Allocate some local variables
        Dim LegA As Integer
        Dim LegB As Integer
        Dim Hyp As Integer
        Dim Triple As String
        Dim Found As Integer
 
        'Find them
        For LegA = 1 To 100
            For LegB = 1 To 100
                For Hyp = 1 To 200
                    If (LegA ^ 2 + LegB ^ 2 = Hyp ^ 2) Then
                        Found = Found + 1
                        Triple = Found & vbTab & LegA & vbTab & LegB & vbTab & Hyp
                        lstTriples.Items.Add(Triple)
                    End If
                Next
            Next
        Next
 

but this generates duplicate triples (3,4,5 and 4,3,5), which the instructor does not want.
I've gone through everything I can think of, and looked at all the different listbox functions and help topics, but I'm at a loss.
Any ideas on how to eliminate the duplicate triples that appear in the listbox?

[SammyB]

You need to rethink your For loops so that you won't have any duplicates. --Sam

[corwood]

You need to rethink your For loops so that you won't have any duplicates. --Sam

Clearly, but could you point me in the direction of something somewhat more substantial? I have (as I mentioned in passing) been racking my brain trying to come up with a solution, but am at a loss (normally these things come pretty quickly).

Thanks for the reply and any future help (that, of course, falls within the limits of morality).

[SammyB]

Clearly, but could you point me in the direction of something somewhat more substantial? I have (as I mentioned in passing) been racking my brain trying to come up with a solution, but am at a loss (normally these things come pretty quickly).

Thanks for the reply and any future help (that, of course, falls within the limits of morality).

As you picked up, I'm trying (as a teacher myself) to make you think of how to solve the problem. A couple more ideas: (1) Do you really need three loops? From trig, you know that the hyp squared = the sum of the squares of the other two sides. (2)Reduce you side limits to something small and write out the variables of the For loop, so that you can see how to make the iterations only cove the possibilities once; for example, when the LeqA For loop is on 2, is there any reason to start the LegB loop at 1? Haven't you already covered that case? Keep smiling! --Sam

[corwood]

Thanks a lot for the help, Sam - I will definitely give it a shot next week when class starts up again.

[SammyB]

Thanks a lot for the help, Sam - I will definitely give it a shot next week when class starts up again.

¿Next week? Don’t procrastinate! Do it now. ;o)>>>

Another good exercise for you: if you write out your loops with some small ending values, so that you can easily go through several iterations, then you should be able to find another (poor, but interesting) solution where you leave your For loops alone and just add a single if statement. Keep smiling, Sam.

[corwood]

'Find them
For LegA = 1 To 100
   For LegB = 1 To 100
      For Hyp = 1 To 200
         If (LegA ^ 2 + LegB ^ 2 = Hyp ^ 2) And LegA < LegB Then
            Found = Found + 1
            Triple = Found & vbTab & LegA & vbTab & LegB & vbTab & Hyp
            lstTriples.Items.Add (Triple)
         End If
      Next
   Next
Next
 

Thaaank you.

[Killer42]

'Find them
For LegA = 1 To 100
  For LegB = 1 To 100
    For Hyp = 1 To 200
      If (LegA ^ 2 + LegB ^ 2 = Hyp ^ 2) And LegA < LegB Then
        Found = Found + 1
        Triple = Found & vbTab & LegA & vbTab & LegB & vbTab & Hyp
        lstTriples.Items.Add (Triple)
      End If
    Next
  Next
Next

Um... Isn't that IF statement kind of pointless? Why check all the lower values of B at all, when you can just start the B loop with a higher value.

Also, I don't understand why the third loop even exists. I though all you needed to know about Hyp is that it's less than 200. So why not just calculate it from the other sides, and test it? Seems to me, this program does more than 200 times as much work as it needs to.

[SammyB]

As Killer says, although your solution works, but it shows that you still don't understand loops. Look back at post #4 in this thread and use it along with Killer's suggestion to come up with a much better solution. --Sam

[Killer42]

As Killer says, although your solution works, but it shows that you still don't understand loops. Look back at post #4 in this thread and use it along with Killer's suggestion to come up with a much better solution. --Sam

Thanks Sam. As you can see, I resisted the temptation to just code it myself and post it. Though not a teacher, I do generally prefer to try and lead the poster to understand the question, if possible. :)

[corwood]

I'm with you on both points -
But I got yelled at when I changed the loop for B to anything but 1 to 100 =/

So quick fix, whatever, as opposed to something like For A = 1 to 100, For B = A to 100

EDIT:
(My teacher loves to talk about the "2 Million Combinations! Wow!" this program goes through)

[Killer42]

...(My teacher loves to talk about the "2 Million Combinations! Wow!" this program goes through)

Let's just hope the teacher doesn't ask you to check them by hand. :)