#!/usr/bin/perl

# This particular code is tested.

use strict;
use warnings;
#
my @CS_CHECKS = (
  '00012345', 'D123470',
  '0000123450', '0000023456',
  '50000123990'
);
my %B_CHECKS = (
  '1234' => 0,
  '12345' => 0,
  '123990' => 0,
  '12399' => 0
);
my %seen;
for my $cn ( @CS_CHECKS )
{
    if ( $cn =~ /^(?:0|5|6)0+(.*)$/ )
    {
        my $bn = $1;
        if ( exists $B_CHECKS{ $bn } )
        {
            print "$bn = $cn\n";
            # $B_CHECKS{ $bn }++;
        }
    }
}