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

Although there are already many solutions to this question, this is mine:

The main feature that differentiates it from the other solutions:

• Only a single loop of complexity O(n)
• Only primitive (integer) temporary variables

The source:

= $bounds) // bottom edge
        {
            $i--;
            $j++;
            $j++;
            $inc = 1;
        }
        if($j >= $bounds) // right edge
        {
            $i++;
            $i++;
            $j--;
            $inc = -1;
        }
        if($j < 0) // left edge
        {
            $j++;
            $inc = 1;
        }
        if($i < 0) // top edge
        {
            $i++;
            $inc = -1;
        }

        $output[] = $input[$bounds * $i + $j];

        $i = $i - $inc;
        $j = $j + $inc;
        $steps++;
    }
    return $output;
}

$a = range(1,25);
var_dump(zigzag($a));

By the way, this sort of algorithm is called "zig zag scan" and is being used heavily for JPEG and MPEG coding.