#! perl -sw
use strict;

sub roundRobin {
	my @q;
	my $next = -1;

	my %self = (
		values	=> sub {
			return @q[@_];
		},
		size	=> sub {
			return scalar @q;
		},
		pos		=> sub {
			return 0+$next;
		},
		add		=> sub {
			return push @q, @_;
		},
		del		=> sub {
			my ($i, %del) = (0);
			@del{@_} = undef;
			@q = grep { exists $del{$_} ? ($next -= $i <= $next) && 0 : ++$i } @q;
			return 1;
		},
		next	=> sub {
			return undef if not @q;
			++$next;
			$next %= @q;
			return $q[$next];
		},
		shuffle => sub {
			my $t;
			$t = $_ + rand @q - $_ and @q[$_, $t] = @q[$t, $_] for (0..$#q);
		},
	);
	return %self;
}

my %rr = roundRobin();

$rr{add}( 'a' .. 'z' );
print $rr{size}(), $rr{values}(0..$rr{size}()-1), $/;
$rr{add}( 'k' .. 'q' );
print $rr{size}(), $rr{values}(0..$rr{size}()-1), $/;
$rr{shuffle}();

while ( my $item = $rr{next}() ) {
	my $pos = $rr{pos}();
	print " @{[$rr{values}( 0 .. $pos -1 )]}".
		"<@{[$rr{values}($pos)]}>".
		"@{[$rr{values}($pos+1..$rr{size}()-1 )]}";
	if (rand(8) < 1) {
		my $new = chr(95+rand 26);
		$rr{add}( $new );
		print "\t --added ", $new;
	}
	if (rand(8) < 1) {
		my $toDelete = $item;
		$toDelete = do {
			$rr{values}( rand( $rr{size}()) )
		} until $toDelete ne $item;
		print "\t--deleting: '", $toDelete;
		$rr{del}( $toDelete );
	}
	print $/;
	select undef, undef, undef, .5;
}


##</code><code>##

C:\test>^Croundrobin
26abcdefghijklmnopqrstuvwxyz
33abcdefghijklmnopqrstuvwxyzklmnopq
 <q>p z e u h j s a k w l o r k g v m x t q d i c m n p b l f y o n
 q<p>z e u h j s a k w l o r k g v m x t q d i c m n p b l f y o n       --added j
 q p<z>e u h j s a k w l o r k g v m x t q d i c m n p b l f y o n j
 q p z<e>u h j s a k w l o r k g v m x t q d i c m n p b l f y o n j
 q p z e<u>h j s a k w l o r k g v m x t q d i c m n p b l f y o n j    --deleting: 'v
 q p z e u<h>j s a k w l o r k g m x t q d i c m n p b l f y o n j       --added _      --deleting: 'e
 q p z u h<j>s a k w l o r k g m x t q d i c m n p b l f y o n j _      --deleting: 'i
 q p z u h j<s>a k w l o r k g m x t q d c m n p b l f y o n j _
 q p z u h j s<a>k w l o r k g m x t q d c m n p b l f y o n j _
 q p z u h j s a<k>w l o r k g m x t q d c m n p b l f y o n j _
 q p z u h j s a k<w>l o r k g m x t q d c m n p b l f y o n j _
 q p z u h j s a k w<l>o r k g m x t q d c m n p b l f y o n j _
 q p z u h j s a k w l<o>r k g m x t q d c m n p b l f y o n j _         --added v
 q p z u h j s a k w l o<r>k g m x t q d c m n p b l f y o n j _ v
 q p z u h j s a k w l o r<k>g m x t q d c m n p b l f y o n j _ v
 q p z u h j s a k w l o r k<g>m x t q d c m n p b l f y o n j _ v       --added b
 q p z u h j s a k w l o r k g<m>x t q d c m n p b l f y o n j _ v b
 q p z u h j s a k w l o r k g m<x>t q d c m n p b l f y o n j _ v b
 q p z u h j s a k w l o r k g m x<t>q d c m n p b l f y o n j _ v b
 q p z u h j s a k w l o r k g m x t<q>d c m n p b l f y o n j _ v b    --deleting: 's
 q p z u h j a k w l o r k g m x t q<d>c m n p b l f y o n j _ v b      --deleting: 'z
 q p u h j a k w l o r k g m x t q d<c>m n p b l f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c<m>n p b l f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c m<n>p b l f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c m n<p>b l f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c m n p<b>l f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c m n p b<l>f y o n j _ v b
 q p u h j a k w l o r k g m x t q d c m n p b l<f>y o n j _ v b         --added b
 q p u h j a k w l o r k g m x t q d c m n p b l f<y>o n j _ v b b
 q p u h j a k w l o r k g m x t q d c m n p b l f y<o>n j _ v b b       --added l
 q p u h j a k w l o r k g m x t q d c m n p b l f y o<n>j _ v b b l
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n<j>_ v b b l     --added g
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j<_>v b b l g
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j _<v>b b l g
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j _ v<b>b l g
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j _ v b<b>l g
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j _ v b b<l>g  --deleting: '_
 q p u h j a k w l o r k g m x t q d c m n p b l f y o n j v b b l<g>
 <q>p u h j a k w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q<p>u h j a k w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p<u>h j a k w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u<h>j a k w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u h<j>a k w l o r k g m x t q d c m n p b l f y o n j v b b l g    --deleting: 'h
 q p u j<a>k w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u j a<k>w l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u j a k<w>l o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u j a k w<l>o r k g m x t q d c m n p b l f y o n j v b b l g
 q p u j a k w l<o>r k g m x t q d c m n p b l f y o n j v b b l g