This solution depends on two factors, how many times does the code run and how much do the length of the strings vary? If the answers are "a lot" and "not much" then here's a faster solution: 
{
  my @cache; # a cache of substring-finding subs
  sub substrings {
    my $string = shift;
    my $length = length $string;

    # use cached sub if we have one
    return $cache[$length]->($string)
      if exists $cache[$length];

    # create sub to find substrings for this length
    my $sub = 'sub { $_ = shift; return (';
    foreach my $length (1..length($string)) {
      foreach my $offset (0..length($string)-$length) {
        $sub .= "substr(\$_,$offset,$length),";
      }
    }
    $sub .= ")};";
    $cache[$length] = eval $sub;

    # and use it
    return $cache[$length]->($string);
  }
}

[download]
Using Benchmark.pm and a test case against random words from /usr/dict/words I found this to be 300% faster over 100,000 iterations. Not bad, but I bet we could do better!

-sam

PS: Has anyone noticed that <code> doesn't deal with hard tabs right? Copy-and-paste from Emacs is unpleasant.

In reply to Re: Finding all substrings by samtregar
in thread Finding all substrings by TheHobbit

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