#!/usr/bin/perl 
use strict; 
 
if (scalar(@ARGV) != 2) { 
    print "Usage: $0 k n\n"; 
    print "  K items from set N\n"; 
    exit 1; 
} 
my ($k,$n) = @ARGV; 
my @Set; 
push @Set, "e$_" for (1 .. $n); 
 
my @Combos = combine($k,\@Set); 
my $i = 0; 
printf "%d) %s\n",++$i, "@$_" for @Combos; 
print "Total Combinations: ",scalar(@Combos),"\n"; 
 
sub combine { 
    my ($k, $s) = @_; 
    my $n = scalar(@$s); 
    my @c = findcombos($k,$n); 
    my @b; 
    foreach my $r (@c) { 
        my @cmb; 
        push @cmb, $s->[$_] for @$r;  
        push @b, [ @cmb ]; 
    } 
    return @b; 
} 
 
sub findcombos { 
    my ($k,$n,$level,$c,$b) = @_; 
    $level ||= 0; 
 
    # initialize arrays 
    unless (ref($c)){ 
        push @$c, $_ for (0 .. $k-1); 
        $b = []; 
    } 
     
    my $i = $level; 
    while ( $i < $n && $c->[$level] < $n ) { 
        if ( $level + 1 == $k ) { 
            #print "@$c\n"; 
            push @$b, [ @$c ]; 
            $c->[$level]++; 
        } 
        else { 
            findcombos($k,$n,$level+1,$c,$b); 
            # advance and reset counters 
            my $v = $c->[$level] + 1; 
            $c->[$_] = $v++ for ($level .. $#$c); 
        } 
        $i++; 
    } 
    return @$b unless $level; 
}