use v5.12;
use warnings;


say my $az = join "","a".."z";
$az x= 100;

my $c;
my $show=0;
sub COUNT {
  $c++;
  say "Step $c matches '",$2 // "","'"
    if $show;
}
$show=0;
for my $l (1..24)

  {
  say "=== Length Str: ",$l;
  my $str = substr $az,0,$l;
  $c = 0;
  $str =~ /( (.) (?{COUNT}) (?1) (*FAIL))/x; 
  say "$l : $c = ", $l*($l+1)/2;
  $c=0;
  $str =~ /( (?: (.) (?{COUNT}) )* (*FAIL) )/x;
  say "$l : $c = ", 2 *$l-1;
}