[RESOLVED] Algo needed: Spiral of numbers based on _n_

**rade** · 12-23-2010, 09:30 AM

Hi,
I'm trying to solve this one assignment we have in PHP.

Based on the given number n, the script is supposed to print out a n*n grid of numbers following the pattern in this image:
http://img222.imageshack.us/img222/4623/79890400.png

In this example the given number n is 4.

Would any of you have an idea for a good algorithm?

**NogDog** · 12-23-2010, 05:43 PM

I couldn't come up with a "good" algorithm, just a more-or-less brute force approach:

PHP Code:


<?php

function spiral($n)

{

   $n = abs((int)$n);

   $result = array();

   $count = 0;

   for($i = 1; $i <= $n; $i++) {

      if($i % 2) {

         for($y = $i, $x = 1; $x <= $i; $x++) {

            $result[$x][$y] = ++$count;

         }

         for($x = $i, $y = $i - 1; $y >= 1; $y--) {

            $result[$x][$y] = ++$count;

         }

      }

      else {

         for($y = 1, $x = $i; $y <= $i; $y++) {

            $result[$x][$y] = ++$count;

         }

         for($x = $i - 1, $y = $i; $x >= 1; $x--) {

            $result[$x][$y] = ++$count;

         }

      }

   }

   return $result;

}

?>

<html><head><title>Test</title>

<style type='text/css'>

table {

   border-collapse: collapse;

   border: solid 2px black;

}

td {

   text-align: center;

   padding: 0.2em;

   border: solid 1px black;

}

</style></head><body>

<?php

$test = range(1,6);

foreach($test as $num) {

   echo "<h3>Test Value: $num</h3>\n";

   $data = spiral($num);

   echo "<table>\n";

   for($y = 1; $y <= $num; $y++) {

      echo "<tr>";

      for($x = 1; $x <= $num; $x++) {

         echo "<td>".$data[$x][$y]."</td>";

      }

      echo "</tr>\n";

   }

   echo "<table>\n";

}

?>

</body></html>