PHP Eight queens

Here is recursive algorithm solving the problem with eight queens which don't threaten each other:

function check( $i )
{
 global $column, $rows, $left_d, $right_d;
 for( $j = 1; $j <= 8; $j++ )
 {
  // check is the row and both diagonals are free
  if( $rows[$j] && $left_d[$i+$j] && $right_d[$i-$j] )
  {
   $column[$i] = $j;//put the qeen on the $i column in the $j position
   
   //set row and diagonals to occupied 
   $rows[$j] = false;
   $left_d[$i+$j] = false;
   $right_d[$i-$j] = false;
   
   // if $i == last column(8) we print the results
   if( $i < 8 )
    check( $i + 1 );
   else
    print_results();
   
   //unset row and diagonals
   $rows[$j] = true;
   $left_d[$i+$j] = true;
   $right_d[$i-$j] = true;
  }
 }
}

function print_results()
{
 global $column;
 foreach( $column as $value )
  echo $value ."&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
 
 echo "<br />\n";
}

for( $i = 1; $i <= 8; $i++ )
 $rows[$i] = true;

for( $i = 2; $i <= 16; $i++ )
 $left_d[$i] = true;
  

for( $i = -7; $i <= 7; $i++ )
 $right_d[$i] = true;

check(1);