从数组中生成字符串范围（1-10,13,16,17-25 ..等）的算法

Question

I'm trying to work out the page range of numbers that exist in an array. I did attempt to search google for it but I only found unrelated posts/pages.

The code I have been working on is:

$numbers = array(1,3,2,4,5,6,7,8,9,11,10,15,14,13,12,16,17,18,19,20,22);

function get_number_ranges($numbers)
{
    $last = null;
    foreach ($numbers as $number) {
        if (is_null($last)) {
            $string = $number;
            $last = $number;
        } elseif ($last + 1 != $number) {
            $string .= '-' . $last . ', ' . $number;
            $last = $number;
        } else {
            $last = $number;
        }
    }

    if ($last == $number) {
        $string .= '-' . $number;
    }

    return $string;
}

and that produces

1-1, 3-3, 2-2, 4-9, 11-11, 10-10, 15-15, 14-14, 13-13, 12-12, 16-20, 22-22

I don't want it to display the duplicate number, so i want it to look like this:

1, 3, 2, 4-9, 11, 10, 15, 14, 13, 12, 16-20, 22

This is so i can represent page ranges when storing history about a document.

Im sure this will be a nice easy one for some1, any help will be greatly received!

Answer 1

Basically you need to remember the first number of each range, and when you come to append the hyphen and the last number, only do so if the last number is different. Something like (untested):

function get_number_ranges($numbers)
{
    $last = null;
    foreach ($numbers as $number) {
        if (is_null($last)) {
            $string = $number;
            $last = $number;
            $first = $number ;                          //Remember first
        } elseif ($last + 1 != $number) {
            if ($first != $last )                       //Only append if different
                $string .= '-' . $last ;
            $string .= ', ' . $number;
            $last = $number;
            $first = $number ;                          //Remember first
        } else {
            $last = $number;
        }
    }

    if ($last == $number && $last != $first) {          //Only if different
        $string .= '-' . $number;
    }

    return $string;
}