This has been asked and answered many times. See Permutations and combinations for a good answer.

-sauoq
"My two cents aren't worth a dime.";

This is in the perlfaq documents. Try

perldoc -q permute
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for a different twist, try merlyn's range-based magical autoincrement.

#!/usr/bin/perl
use strict;
use warnings;
$|++;

my $alphaGen = sub { scalar glob "{A,B,C}{A,B,C}" };

print $_,$/ while $_ = $alphaGen->();
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i figure if this is homework, you'd never get away with submitting this answer -- but you (and others) might learn this sweet little trick.

~Particle *accelerates*

  my @set = qw(A B C);
  my @list;
  foreach my $one (@set) {
    foreach my $two (@set) {
       push @list,"${one}$two";
    }
  }
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This is called a cartesian product incidentally.

This will have a problem, if the set is ("a", "a", "a", "a", "b"), then you will repeat combinations unnecessarily.

Sets, by definition, don't have duplicate elements.

Collections which permit duplicate elements are known as "bags" or "multisets."

-sauoq
"My two cents aren't worth a dime.";

Maybe not. It depends on whether the duplicates are significant or not. That wasn't specified in the question.

-pete
"Worry is like a rocking chair. It gives you something to do, but it doesn't get you anywhere."

use strict;

my @chars = ("a", "a", "b", "c");

my %non_repeat;
foreach (@chars) {
    if (exists($non_repeat{$_})) {
        $non_repeat{$_} = 2;
    } else {
        $non_repeat{$_} = 1;
    }
}

my @combinations;
my ($first, $second);
my @keys = keys %non_repeat;
my ($index1, $index2);
for ($index1 = 0; $index1 <= $#keys; $index1 ++) {
    if ($non_repeat{$keys[$index1]} == 2) {
        push @combinations, $keys[$index1] x 2;
    }
    for ($index2 = $index1 + 1; $index2 <= $#keys; $index2 ++) {
        push @combinations, $keys[$index1] . $keys[$index2];
        push @combinations, $keys[$index2] . $keys[$index1];
    }
}

print join(",", @combinations);
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my @initial_array = ("A","B","C");
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Good Luck

enlil

This may help you. The code below generates a array list that eliminates redundant data.

my @set = qw(A B C D A);

my @list;

my $elm;

my $count=0;

foreach my $one (@set) {

foreach my $two (@set) {

$elm ="$one"."$two";

foreach $list(@list){$count++ if ($list eq elm);}

push @list,"$one$two" if($count eq 0);

}

}

Cheers!!!!

Anandatirtha

Correction

foreach $list(@list){$count++ if ($list eq $elm);}

Anandatirtha