#!perl -w
use strict;
# kenhirsch at myself.com  2002-08-23

my $r = shift or die "usage: combinations r a b c d e ...\n";
my @out = combinations($r, \@ARGV);

for (@out) {
  print join(" ", @{$_}), "\n";
}

# From Algorith L in Knuth Vol. 4  Sec 7.2.1.3 (not yet published)
sub combinations {
  my ($t, $arrayref) = @_;
  my @c = 0 .. $t-1;
  my @range = reverse @c;
  my $j;
  my @result;
  $c[$t] = scalar(@{$arrayref});
  $c[$t + 1] = 0;
  do {
    push @result, [@{$arrayref}[@c[@range]]];
    for ($j=0; $c[$j] + 1 == $c[$j+1]; $j++) {
      $c[$j] = $j;
    }
    $c[$j]++;
  } while ($j < $t);
  return @result;
}

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In reply to A non-recursive solution by Thelonius
in thread Combinatorics by ezekiel

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