今天遇到的一份面试题

function Circle($n) {
  $k = $n % 2;
  $ar = array();
  for($i=0; $i<$n; $i++)
    $ar[$i] = array_fill(0, $n, 0);
  $p = 1;
  $x = 0;
  $y = 0;
  $m = 0;
  $len = $n * $n;
  while($p < $len) {
    $x = $y = $m;
    while($x < $n) $ar[$y][$x++] = $p++;
    $x--;
    $y++;
    while($y < $n) $ar[$y++][$x] = $p++;
    $y--;
    $x--;
    while($x >= $m) $ar[$y][$x--] = $p++;
    $x++;
    $y--;
    $m++;
    while($y >= $m) $ar[$y--][$x] = $p++;
    $n--;
  }
  if($k) $ar[$y+1][$x+1] = $p;

  $r = '';
  foreach($ar as $v)
    $r .= '';
  return $r.'
' . join('
', $v) . '
';  
}
for($i=2;$i<30;$i++){  
    $html .= Circle( $i );  
    $html .='
';  
}  
?>