The regex engine is quite adept at backtracking to find all inputs that satisfy a set of conditions. The shortest solution should be a regex one. 

my $str = 'aabcdabcabcecdecd';

local our %counts;
$str =~ /
   (.{2,})   # or (.+)
   (?(?{ !$counts{$1} })(?=.*\1))
   (?{ ++$counts{$1} })
   (?!)
/x;

use Data::Dumper;
print Dumper \%counts;

[download]

Update:
(?(?{ !$counts{$1} })(?=.*\1))
might be more efficient as
(?> (?(?{ !$counts{$1} })(?=.*\1)) )

Update: The above doesn't work. $str='ababa' fails. My simpler version doesn't suffer from this bug.

In reply to Re: how to count the number of repeats in a string (really!) by ikegami
in thread how to count the number of repeats in a string (really!) by blazar

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