编辑:对于我的错误我感到很抱歉。我忽视了在countit(x, q{})
中使用my
变量是一个大错误。这个字符串在Benchmark模块内被评估,而@str在那里是空的。这个解决方案并不像我所展示的那样快。请查看下面的更正。我再次道歉。
Perl可以很快:
use strict;
use warnings;
package LCP;
sub LCP {
return '' unless @_;
return $_[0] if @_ == 1;
my $i = 0;
my $first = shift;
my $min_length = length($first);
foreach (@_) {
$min_length = length($_) if length($_) < $min_length;
}
INDEX: foreach my $ch ( split //, $first ) {
last INDEX unless $i < $min_length;
foreach my $string (@_) {
last INDEX if substr($string, $i, 1) ne $ch;
}
}
continue { $i++ }
return substr $first, 0, $i;
}
sub LCP2 {
return '' unless @_;
my $prefix = shift;
for (@_) {
chop $prefix while (! /^\Q$prefix\E/);
}
return $prefix;
}
1;
测试套件:
use strict;
use warnings;
Test::LCP->runtests;
package Test::LCP;
use base 'Test::Class';
use Test::More;
use Benchmark qw(:all :hireswallclock);
sub test_use : Test(startup => 1) {
use_ok('LCP');
}
sub test_lcp : Test(6) {
is( LCP::LCP(), '', 'Without parameters' );
is( LCP::LCP('abc'), 'abc', 'One parameter' );
is( LCP::LCP( 'abc', 'xyz' ), '', 'None of common prefix' );
is( LCP::LCP( 'abcdefgh', ('abcdefgh') x 15, 'abcdxyz' ),
'abcd', 'Some common prefix' );
my @str = map { chomp; $_ } <DATA>;
is( LCP::LCP(@str),
'file:///home/gms8994/Music/', 'Test data prefix' );
is( LCP::LCP2(@str),
'file:///home/gms8994/Music/', 'Test data prefix by LCP2' );
my $t = countit( 1, sub{LCP::LCP(@str)} );
diag("LCP: ${\($t->iters)} iterations took ${\(timestr($t))}");
$t = countit( 1, sub{LCP::LCP2(@str)} );
diag("LCP2: ${\($t->iters)} iterations took ${\(timestr($t))}");
}
__DATA__
file:///home/gms8994/Music/t.A.T.u./
file:///home/gms8994/Music/nina%20sky/
file:///home/gms8994/Music/A%20Perfect%20Circle/
测试套件结果:
1..7
ok 1 - use LCP
ok 2 - Without parameters
ok 3 - One parameter
ok 4 - None of common prefix
ok 5 - Some common prefix
ok 6 - Test data prefix
ok 7 - Test data prefix by LCP2
这意味着使用 substr
的纯 Perl 解决方案比您的测试用例中Roy 的解决方案快约20%,每个前缀查找大约需要50微秒。除非您的数据或性能期望更大,否则不必使用 XS。