Sorting PHP arrays with substrings

sameer — Thu, 10 Dec 2009 12:35:17 +0000

A couple of days back I encountered the following request on a forum for sorting a single dimensional array. The programmer wanted to sort the following array by the substring after the colon. For example ‘CDF’ in the string ’66345:CDF’. Those values that do not have any colon should be ignored and pushed to the end of the array. Also, the length of the strings are not constant.

$values = array("66345:CDF", "61179:HGT", "64146:ABA",
                "68768:BNG", "68015:ZCZ", "80231:LPO",
                "64146:QWP", "68736:HHB", "86801:MNV",
                "80178:OIU", "80178:ASE", "88178:BRT",
                "801782OIU", "801378ASE", "881578BRT");

A quick solution was the following. But I’m sure that this is not the fastest, as a matter of fact it is quite slow for larger arrays.

 

 
$values = array("66345:CDF", "61179:HGT", "64146:ABA",
                "68768:BNG", "68015:ZCZ", "80231:LPO",
                "64146:QWP", "68736:HHB", "86801:MNV",
                "80178:OIU", "80178:ASE", "88178:BRT",
                "801782OIU", "801378ASE", "881578BRT");
 
 
function my_cmp($a, $b)
{
    $pieces_a = explode(":", $a);
    $pieces_b = explode(":", $b);
 
    if(!isset($pieces_a[1]) && isset($pieces_b[1])) {
        return 1;
    }
    elseif(!isset($pieces_b[1]) && isset($pieces_a[1])) {
        return -1;
    }
    elseif(!isset($pieces_a[1]) && !isset($pieces_b[1])) {
        return 0;
    }
 
    return strcasecmp($pieces_a[1], $pieces_b[1]);
}
 
usort($values, "my_cmp");
 
?>

So what will be the fastest algorithm for the same?

Luhn algorithm for validating credit cards

sameer — Wed, 09 Jul 2008 14:32:19 +0000

The Luhn algorithm also known as the “modulus 10″ or “mod 10″ algorithm, is a checksum formula which can be used to validate credit card numbers. Developed in the 1950′s by IBM scientist Hans Peter Luhn and described in U.S. Patent 2,950,048. A PHP implementation is shown below.

 
function LuhnCheck($strDigits)
{
    $sum = 0;
    $alt = false;
    for($i = strlen($strDigits) - 1; $i >= 0; $i--) 
    {
        if($alt)
        {
           $temp = $strDigits[$i];
           $temp *= 2;
           $strDigits[$i] = ($temp > 9) ? $temp = $temp - 9 : $temp;
        }
        $sum += $strDigits[$i];
        $alt = !$alt;
    }
    return $sum % 10 == 0;
}

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Sorting PHP arrays with substrings

Luhn algorithm for validating credit cards