# more update: this is the tested version now!!

sub CountSubstrings { # $string1, $string2, $substr_length
    my $l = pop @_;
    my %found = ();
    my %match = ();
    my $first = 2;
    my $string1 = $_[0];
    for my $string ( @_ ) {
        $first --;
        my $ls = length( $string );
        my $limit = $ls - $l + 1;
        for ( my $i = 0; $i < $limit; $i++ ) {
            my $sbstr = substr( $string, $i, $l );
            $first or defined ( $match{$sbstr} ) && next();
            $found{ $sbstr }{ $string } ||= 1;
            $first and next;;
            defined ( $found{ $sbstr }{ $string1 } )
              and $match{ $sbstr } = 1;
        }
    }
    Count( keys %match );
}
sub Count { 1+$#_ };

[download]
Description of alggorithm: Store all substrings of string 1 of the given length in subhash $found{ $string1 }; do the same for string 2 but in addition lookup in the first hash and record any matches in the %match hash. The suggested opportunities for optimisation include (a) only need to check matches for the substring iteration of the second string. (b) only need to build the substring for string 2 if there is no match found in the match hash.

-M

Free your mind

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

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