Create contact using custom field in civicrm 4.0 (civicrm API)

Create contact using custom field in prifile when event registration.
Create Contacts using API in civicrm 4.0 in drupal 7 on post process.
 If the contact exists then it o/p that contacts id & if not exists then it create new contact & gives the o/p .

function eventType_customPath_civicrm_postProcess( $formName, &$form ){
    if( $formName == 'CRM_Event_Form_Registration_Confirm' ){
        $participantContact = $form->getVar('_params');
        $participantFirstNameId = array( 'custom_11', 'custom_15', 'custom_19' );   /* add custom first name Id */
        $participantLastNameId = array( 'custom_12', 'custom_16', 'custom_20' );    /* add custom last name Id */
        $participantEmailId = array( 'custom_13', 'custom_17', 'custom_21' );       /* add custom email Id */
        $participant = array( );
        for( $count = 0; $count < 3; $count++ ) {
            $participant[ $count ][ 'firstname' ] = $participantContact[ $participantFirstNameId [ $count ] ];
            $participant[$count]['lastname'] = $participantContact [ $participantLastNameId [ $count ] ];
            $participant[$count]['email'] = $participantContact [ $participantEmailId [ $count ] ];
        }
        require_once "api/api.php";
        foreach( $participant as $participantKey => $participantValue ){
            if( !empty( $participantValue['firstname'] ) && !empty( $participantValue['lastname'] ) ) {
                $searchContact = array ( 'first_name' => $participantValue['firstname'] , 'last_name' => $participantValue['lastname'], 'version' =>3 );
                $contact = civicrm_api( 'Contact', 'Get', $searchContact );
                if(isset($contact['value'])){
                    $contactId[]['contact_a'] = $contact['id'];
                }else{
                    $createContact = array ( 'first_name' => $participantValue['firstname'] , 'last_name' => $participantValue['lastname'], 'email' => $participantValue['email'],'contact_type' => 'Individual', 'version' =>3 );
                    $contact = civicrm_api( 'Contact', 'Create', $createContact );
                    $contactId[]['contact_a'] = $contact['id'];
                }
            }
        }
    }
}

Gives the o/p as 

$contact 

[0]=>

          array(

                   [contact_a] => 123

                 )

[1] => array(

                    [contact_a] => 124

                    )