Yet another WTDI:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $data   = '11122222344456788899';

my @data   = split(//, $data);
my $accum  = {};
my @buffer = ();

push(@buffer, shift(@data));
  
while (@data) {
  push(@buffer, shift(@data));
  if($buffer[0] == $buffer[1]) {
    $accum->{$buffer[0]}++;
  }
  shift(@buffer);
}

print Dumper($accum);
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