I throw my hat into the ring with my recursive implementation. I think it could perform reasonably well, since it is a divide-and-conquer type solution.

I'm not sure how it will stand up to the hash-based solutions, and there might be some "correctness" issues...

For the bonus, though, mine increments the count for *any* length of matching substrings.

There are probably many opportunities for optimizations here... please offer criticism.


#! perl -w
use strict;

my $hits = 0;

sub common_substr {
  my($s1, $s2) = @_;

  print qq(s1 = $s1, s2 = $s2\n);
  
  ($s1, $s2) = ($s2, $s1) if length($s2) < length($s1);
  if ($s1 eq $s2) {
    $hits++; 
    return if length($s1) == 1;
  }      
  my %hash = map { $_ => 1 } split(//, $s1);
  my $arr = [];
  for my $s (split(//, $s2)) {
    push(@$arr, $s) if ! exists($hash{$s});
  }
  my $splitters = join('|', @$arr);
  for my $s (split(/$splitters/, $s2)) {
    common_substr($s, $s1);          
  }
}

common_substr("abcef", "abcdef");
print "hits = $hits\n";

[download]

Where do you want *them* to go today?

In reply to Re: Challenge: Fast Common Substrings by thezip
in thread Challenge: Fast Common Substrings by Limbic~Region

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