#!/usr/bin/perl
use warnings;
use strict;
use Benchmark qw(cmpthese timethese);

my @test = ([ qw(fooabc123 fooabc321 foobca232) ],
            [ qw(abcfoo123 bcafoo321 foo123abc) ],
            [ qw(foo bor boz bzo) ]);

for (@test) {
     die "regex,index" unless lcs_regex(@{$_}) eq lcs_index(@{$_});
     die "index,buk"   unless lcs_index(@{$_}) eq lcs_buk(@{$_});
}

my $result = timethese(-5, {
    'regex' => sub { lcs_regex(@{$_}) for @test },
    'index' => sub { lcs_index(@{$_}) for @test },
    'buk'   => sub {   lcs_buk(@{$_}) for @test },
});

cmpthese $result;

sub lcs_regex {
    my $substr = $_[0];
    my $len = length $_[0];
    my $off = 0;

    while ($substr) {
        my @matches = grep /\Q$substr/, @_;
        #printf "%s%-".(length($_[0])-$off)."s matches %d\n",
        #       " " x $off, $substr, scalar @matches;

        last if @matches == @_;

        $off++;
        $len-- and $off=0 if $off+$len > length $_[0];

        $substr = substr $_[0], $off, $len;
    }

    return $substr;
}

sub lcs_index {
    my $substr = $_[0];
    my $len = length $_[0];
    my $off = 0;

    while ($substr) {
        my @matches = grep { -1 != index $_, $substr } @_;
        #printf "%s%-".(length($_[0])-$off)."s matches %d\n",
        #       " " x $off, $substr, scalar @matches;

        last if @matches == @_;

        $off++;
        $len-- and $off=0 if $off+$len > length $_[0];

        $substr = substr $_[0], $off, $len;
    }

    return $substr;
}

sub lcs_buk {
    my $strings = join "\0", @_;
    my $lcs;
    for my $n ( 1 .. length $strings ) {
        my $re = "(.{$n})" . '.*\0.*\1' x ( @_ - 1 );
        last unless $strings =~ $re;
        $lcs = $1
    }
    return $lcs;
}

##</code><code>##

Benchmark: running buk, index, regex for at least 5 CPU seconds...
       buk:  6 wallclock secs ( 5.31 usr +  0.01 sys =  5.32 CPU) @ 1973.50/s (n=10499)
     index:  5 wallclock secs ( 5.29 usr +  0.01 sys =  5.30 CPU) @ 3023.77/s (n=16026)
     regex:  6 wallclock secs ( 5.29 usr +  0.00 sys =  5.29 CPU) @ 931.00/s (n=4925)
        Rate regex   buk index
regex  931/s    --  -53%  -69%
buk   1973/s  112%    --  -35%
index 3024/s  225%   53%    --