use strict;
use warnings;
use Benchmark qw( cmpthese timethese );
use constant TARGET => 1_389_019_170;

my $r = timethese
(
    5,
    {
        use_re  => sub { my $ans1 =  use_re();
                            $ans1 == TARGET or die $ans1; },

        use_qr  => sub { my $ans2 =  use_qr();
                            $ans2 == TARGET or die $ans2; },

        use_str => sub { my $ans3 =  use_str();
                            $ans3 == TARGET or die $ans3; }
    }
);

cmpthese $r;

sub use_re
{
    for (my $n = 1_010_101_030; $n <= 1_389_026_623; )
    {
        my $s  = $n * $n;
        return   $n if $s =~ /^1\d2\d3\d4\d5\d6\d7\d8\d900$/;
           $n += 40;
           $s  = $n * $n;
        return   $n if $s =~ /^1\d2\d3\d4\d5\d6\d7\d8\d900$/;
           $n += 60;
    }

    die;
}

sub use_qr
{
    my $re = qr/^1\d2\d3\d4\d5\d6\d7\d8\d900$/;

    for (my $n = 1_010_101_030; $n <= 1_389_026_623; )
    {
        my $s  = $n * $n;
        return   $n if $s =~ $re;
           $n += 40;
           $s  = $n * $n;
        return   $n if $s =~ $re;
           $n += 60;
    }

    die;
}

sub use_str
{
    my $str = '^1\d2\d3\d4\d5\d6\d7\d8\d900$';

    for (my $n = 1_010_101_030; $n <= 1_389_026_623; )
    {
        my $s  = $n * $n;
        return   $n if $s =~ /$str/;
           $n += 40;
           $s  = $n * $n;
        return   $n if $s =~ /$str/;
           $n += 60;
    }

    die;
}