Can the for loop be eliminated from this piece of PHP code?

Question

I have a range of whole numbers that might or might not have some numbers missing. Is it possible to find the smallest missing number without using a loop structure? If ther

Answer 1

I honestly don't get why you wouldn't want to use a loop. There's nothing wrong with loops. They're fast, and you simply can't do without them. However, in your case, there is a way to avoid having to write your own loops, using PHP core functions. They do loop over the array, though, but you simply can't avoid that.
Anyway, I gather what you're after, can easily be written in 3 lines:

function highestPlus(array $in)
{
    $compare = range(min($in), max($in));
    $diff = array_diff($compare, $in);
    return empty($diff) ? max($in) +1 : $diff[0];
}

Tested with:

echo highestPlus(range(0,11));//echoes 12
$arr = array(9,3,4,1,2,5);
echo highestPlus($arr);//echoes 6

And now, to shamelessly steal Pé de Leão's answer (but "augment" it to do exactly what you want):

function highestPlus(array $range)
{//an unreadable one-liner... horrid, so don't, but know that you can...
     return min(array_diff(range(0, max($range)+1), $range)) ?: max($range) +1;
}

How it works:

$compare = range(min($in), max($in));//range(lowest value in array, highest value in array)
$diff = array_diff($compare, $in);//get all values present in $compare, that aren't in $in
return empty($diff) ? max($in) +1 : $diff[0];
//-------------------------------------------------
// read as:
if (empty($diff))
{//every number in min-max range was found in $in, return highest value +1
    return max($in) + 1;
}
//there were numbers in min-max range, not present in $in, return first missing number:
return $diff[0];

That's it, really.
Of course, if the supplied array might contain null or falsy values, or even strings, and duplicate values, it might be useful to "clean" the input a bit:

function highestPlus(array $in)
{
    $clean = array_filter(
        $in,
        'is_numeric'//or even is_int
    );
    $compare = range(min($clean), max($clean));
    $diff = array_diff($compare, $clean);//duplicates aren't an issue here
    return empty($diff) ? max($clean) + 1; $diff[0];
}

Useful links:

• The array_diff man page
• The max and min functions
• Good Ol' range, of course...
• The array_filter function
• The array_map function might be worth a look
• Just as array_sum might be