Re: How can one generate all possible combinations with reference to string positions?

[kennethk]

I observe that your L's and H's don't move, and that the last two terms are dictated by the first two. This means your pattern can be generated fairly simply with

#!/usr/bin/perl -w
use strict;

for my $h (1 .. 2) {
    for my $l (1 .. 2) {
        printf "L%dH%dL%dH%d\n", $l, $h, 3-$l, 3-$h;
    }
}

Obviously, scaling this up to 500 positions and 10 groups is non-trivial, but should be doable similarly. If you need arbitrary complexity, you'll probably want to generate a work queue rather than having fixed nested for loops.

[supriyoch_2008]

Hi kenneth,

Thanks for the script. It works nicely. I shall be glad if you kindly explain how to use and change the code 3-$l, 3-$h. Does it have any relationship with the number of L and H in the string following printf? Do the $h (1..2) and $l (1..2) refer to 2 levels each for H and L? Actually I tried to learn making some alterations in the script like 4-$l, 5-$h, $h(1..3), $l(1..4) etc.in appropriate places but I could not understand. This is because I donot know why the terms are used and how to change them. I hope you won't mind explain the terms. Please suggest me some reference texts for further study.

[kennethk]

The transform 3-$l only works if you are working with 1 and 2 as your permuted set; it happens that for that set 3-$l is equivalent to "the member of the set that is not $l". If you need any degree of flexibility, you should follow the code in Re: How can one generate all possible combinations with reference to string positions?, subject to BrowserUK's comments.