@array = (2 ,4, 3, 8, 9, 12, 13, 20, 18, 7 );

my $c=0;
@sort_a_pos = sort {$a->[1]<=>$b->[1]} map { [$c++ => $_] } @array;

$pct = @array  / 10;

$_->[1] = "B" for @sort_a_pos[0 .. $pct];
$_->[1] = "-" for @sort_a_pos[$pct+1 .. $#array-$pct-1];
$_->[1] = "A" for @sort_a_pos[$#array-$pct .. $#array];

@finalarray  = map {$_->[1] } sort { $a->[0] <=> $b->[0] } @sort_a_pos;

print "@finalarray";