Here's the no regex simple iterator version. Just for comparison as I suspect that there is a faster method.

use Data::Dumper;
my $string ='    aaaa    bbbbccccccccbbbb   aaaabbbbbcdddddddddddddddd
+dddd';
my (@res, $c, $p, $i);
$p = 0;
$c = substr($string,$p,1);
for ($i=1; $i<length($string); $i++) {
  next if ($c eq substr($string,$i,1));
  push (@res, [$c,$p,($i-$p)]);
  $c = substr($string,$i,1);
  $p = $i;
}
push (@res, [$c,$p,($i-$p)]);
Dumper (\@res);
[download]

Dingus

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