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John Lockheart
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Joined: Oct 13, 2006
Posts: 115
If you have a Range thats inclusive (all ints between low and high)...which will have a simple isEmpty() method that returns true if a range is empty and false otherwise ([0,0] is valid, so a way is needed to represent an empty range), and an intersection(Range other) method that returns a new range equal to the intersection between this range and the other, or empty if they don't intersect. Its a question for a class which I dont understand...Don't even know where to begin because I dont understand this whole range and intersection concept. Any help or a nudge in the right direction would be appreciated.

and some examples...if you have [3,6] & [4,10] intersection = [4,6] and if you have [10,20] & [30,40] intersection = empty
Keith Lynn
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Joined: Feb 07, 2005
Posts: 2367
Do you mean that you don't understand what intersection means?

In one of your examples, [3,6] & [4,10] = [4,6].

What that means is that if you look at the numbers between 3 and 6, 3,4,5,6, and the numbers between 4 and 10, 4,5,6,7,8,9,10, then which numbers are in common to the two ranges? In this case, the numbers between 4 and 6.
John Lockheart
Ranch Hand

Joined: Oct 13, 2006
Posts: 115
haha, i guess i'm a little slow sometimes. When i see questions like that I immediately think "lines, so i need 4 points, 2 ranges only gives me two points". So than i guess the code i'm looking for is going to be pretty simple. i'll give it a try and maybe post it if i have problems
John Lockheart
Ranch Hand

Joined: Oct 13, 2006
Posts: 115
but which what range should i specify to indicate it's an empty range. Like if they don't intersect, instead of returning the empty range i.e [30,20], returning a preset empty range like [0,0]. But thats a valid entry...any thoughts??
Paul Clapham

Joined: Oct 14, 2005
Posts: 19357

You have an isEmpty() method. So I don't see any point in fiddling with Ranges like [30,20] just because they are empty. Just return that and make sure its isEmpty() method returns true.
Gavin Tranter
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Joined: Jan 01, 2007
Posts: 333
Hi all,
I was wondering if this (Range) could be considered as an extenstion of a Set.

I was thinking that set A could be the Range of numbers between [x,y] and set B could be the Range numbers betwen [w,z].

Conceptually I think its quite neat. Practically, you would have to extend Set to Range providing a constructor that took your begin and end range values, this would have to use brute force to file the Range with the numbers in the range. Its a bit messy from the practical stand point.

Of course it dosnt help with understanding the problem of what an intersection is.

Just that intersection shouts Sets in bright pink neon, I am sure they wouldnt like you just Extending/Implementing the Set interface. But looking up Sets (and Venn Diagrams)in a Maths book, or checking out the Java trail on the collections frame work over on Sun Java Site might help you out.

It is sorta covered in the JavaRanch Style Guide.
subject: Ranges[x,y]????