use strict;
use warnings;
use List::Util 'sum';
use Data::Dump qw[ pp ];

sub gen {
    my $href = shift;
    my %score = %$href;
    my $norm = sum values %score;
    my @series;
    
    for (1 .. $norm) {
        my ($max, $elem) = 0;
        for (keys %score) {
            ($max, $elem) = ($score{$_}, $_) if $score{$_} >= $max;
            $score{$_} += $href->{$_};
        }
        push @series, $elem;
        $score{$elem} -= $norm;
    }
    
    return \@series;
}

pp gen( { A => 4, B => 2, C => 3, D => 1 } );
pp gen( { A => 5, B => 4, C => 3, D => 2, E => 1 } );

##</code><code>##

["A", "C", "B", "A", "D", "C", "A", "B", "C", "A"]
["A" .. "D", "A", "B", "E", "A", "C", "B", "A", "D", "C", "B", "A"]
##</code><code>##

use strict;
use warnings;
use List::Util 'sum';

sub measure {
    my @series = @_;
    my %count;
    $count{$_}++ for @series;
    my $norm = sum values %count;
    $_ /= $norm for values %count;
    my %score = %count;

    my $metric = 0;
    for my $elem (@series) {
        $score{$elem} -= 1;
        for (keys %score) {
            $metric += $score{$_}**2;
            $score{$_} += $count{$_};
        }
    }
    
    return $metric/@series;
}

print measure("A", "C", "B", "A", "D", "C", "A", "B", "C", "A"), "\n";
print measure("A", "C", "B", "A", "C", "D", "A", "B", "C", "A"), "\n";
print measure("A", "A", "A", "A", "B", "B", "C", "C", "C", "D"), "\n";
##</code><code>##

0.37
0.37
3.45