Combinational Algorithm

Veritas · 17 Apr 2006 at 16:41

I'm trying to code a combinational algorithm and I'm struggling a little bit.

I am looking to generate every possible, unique 4 digit array from these 10 numbers.
eg.

numbers = [1,2,3,4,5,6,7,8,9,10]
length = 4

Output:
1,2,3,4
1,2,3,5
1,2,3,6
...
...
...
6,7,1,2
6,7,1,3
etc
etc

Can anyone offer any advice?

Beansprout · 17 Apr 2006 at 16:47

Combinations and permutations...I can't remember a thing about these

For combinations, are 1,1,1,2 and 2,1,1,1 counted as different results or is that permutations?

Veritas · 17 Apr 2006 at 16:53

Sorry, I should have been more clear

I only want unique numbers.

ie.

4,7,2,3
7,2,9,1

but not

1,1,6,8
4,5,1,4
etc

Hope that makes more sense

Beansprout · 17 Apr 2006 at 16:55

Cool - so using that example, does 7,2,9,1 count as a separate result to 7,2,1,9? ie, does the order matter? (that's the question I meant to ask at first)

Just trying to refresh my brain here with all this stuff in general so that I stand a chance of helping

Veritas · 17 Apr 2006 at 16:57

It would be good if they were treated the same in order that the number of combinations is less, but to be honest it doesn't matter that much if 4,9,7,1 is said to be the same as 9,4,7,1.

Beansprout · 17 Apr 2006 at 17:10

Ah cool. I remember all this now

I have a handy page here which may help. There's a section on there which'll show all the combinations - I don't want to give you the answer but I haven't found a tutorial as such on the concepts.

And it's written in un-commented obscure Javascript anyway so to interpret it (I believe the relevant function from the source code is doperm() ) you'll need to have a rough idea of the theories anyway, which I guess you do, or you wouldn't be trying/having to do this

Visage · 17 Apr 2006 at 17:54

EDIT: nonsense

Veritas · 17 Apr 2006 at 18:08

Beansprout said:
Ah cool. I remember all this now

I have a handy page here which may help. There's a section on there which'll show all the combinations - I don't want to give you the answer but I haven't found a tutorial as such on the concepts.

And it's written in un-commented obscure Javascript anyway so to interpret it (I believe the relevant function from the source code is doperm() ) you'll need to have a rough idea of the theories anyway, which I guess you do, or you wouldn't be trying/having to do this

Thanks, that helped a lot.

I'm going to try coding my own in C# based on that now. I'll post the code if/when I get it working

Lagz · 17 Apr 2006 at 20:03

This can be done very concisely and neatly using recursion (I wrote this program in 3 lines of ML once. . .but I cant remember how

).