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

  1. #1
    Join Date
    Nov 2006
    Location
    Ekenäs, Finland
    Posts
    17

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

    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?

  2. #2
    Join Date
    Aug 2004
    Location
    Ankh-Morpork
    Posts
    22,284
    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>
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  3. #3
    Join Date
    Nov 2006
    Location
    Ekenäs, Finland
    Posts
    17

    resolved

    Thank you NogDog, the solution is Perfect!!
    Great job!

    Happy holidays!
    // Rade

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