My last contribution to this, just cos I am playing with closures and i was having fun.

The following is an "OO" solution, with an interesting testcase to prove it works. 

#! 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;
}

[download]

Its worth running just to see the testcase in action, leastwise I think so:)

I've attach a short snippet of output here.

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

[download]
Well It's better than the Abottoire, but Yorkshire!

In reply to Re: round-robin on varying sequence by BrowserUk
in thread round-robin on varying sequence by dpuu

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