Zig-zag scan an N x N array

Question

I have a simple array. The array length always has a square root of an integer. So 16, 25, 36 etc.

$array = array(\'1\', \'2\', \'3\', \'4\' ... \'25\');
         


        

Answer 1

One more PHP solution, using just for and if, traverses array only once

function waveSort(array $array) {

    $elem = sqrt(count($array));

    for($i = 0; $i < $elem; $i++) {
        $multi[] = array_slice($array, $i*$elem , $elem);
    }

    $new = array();
    $rotation = false;
    for($i = 0; $i <= $elem-1; $i++) {
        $k = $i;
        for($j = 0; $j <= $i; $j++) {
            if($rotation)
                $new[] = $multi[$k][$j];
            else
                $new[] = $multi[$j][$k];
            $k--;
        }   
        $rotation = !$rotation;
    }

    for($i = $elem-1; $i > 0; $i--) {
        $k = $elem - $i;

        for($j = $elem-1; $j >= $elem - $i; $j--) {

            if(!$rotation)
                $new[] = $multi[$k][$j];
            else
                $new[] = $multi[$j][$k];
            $k++;
        }   
        $rotation = !$rotation;
    }

    return $new;
}

$array = range(1, 25);
$result = waveSort($array);
print_r($result);

$array = range(1, 36);
$result = waveSort($array);
print_r($result);

Here it is in action