Program that prints star pattern

Question

I have a program that prints the star pattern.

Starr Pattern is:

          * 
          * 
          * 
          * 
  * * * * * * * * * 
          * 
          * 
          * 
          * 

My code is:

$n=5;

for($i=0; $i<$n; $i++){

  for($k=$n-$i; $k>0; $k--){
      echo ' '.' ';
  }
  for($j=0; $j< ($tot = $i+1); $j++){

      if($i==$j && $tot<$n){
        echo '* ';
      }else{
          if($tot<$n){
            echo ' '.' ';  
          }else{
             echo '* ';
          }
      }


  }

  if($i == ($n-1)){
      for($l=$n-1; $l>0;$l--){
         echo '* ';      
       }
     }  
  echo '<br/>';

}

for($i=0;$i<$n;$i++){
  for($k=$n-$i; $k>0; $k--){
      echo ' '.' ';
  }

  for($j=0; $j< ($tot = $i+1); $j++){

      if($i==$j && $tot<$n){
        echo '* ';
            }else{
              echo ' '.' '; 
            }
    }
  echo '<br/>';
}

My question is that how can I calculate the complexity of this code?

And also Is there a good way to reduce loops?

Answer 1

It looks nice. Can you please make me understand how it works

For example

 function f($n){$s='';$b=str_pad('*',($m=$n*2+1),' ',2);for($i=0;$i<$m;++$i)$s.=($i==$n)?str_repeat('*',$m):$b;return chunk_split($s, $m);}

Output

     *     
     *     
     *     
     *     
     *     
***********
     *     
     *     
     *     
     *  

Sandbox

Let me write it in a way that is easier to see

$n = 5;
$row_len = $n*2+1;
$output = '';
//pad $n spaces on each side of *
$default = str_pad('*',$row_len,' ',STR_PAD_BOTH); //is = "     *     "

//loop once for each vertical row (same as width)
for($i=0;$i<$row_len;++$i){
    if($i==$n){
        //do the center line all *'s
        $output .= str_repeat('*',$row_len);//is = "***********"
    }else{
        //use the default line from above
        $output .= $default;
    }
}

//now we have a single line that is the length squared so we can chunk it
//into equal parts, to make a square
echo chunk_split($output, $row_len);  //is = "     *          *     ***********"

Sandbox

Basically we can create the " * " row by using string pad. Because we can pad spaces on both sides of a * up to the length of a row ($n*2)+1.

Then the center row, is just * so we can use string repeat to the length of the row for that line.

Last we take our big huge line of spaces and * and split it into chunks (\n) on the length of our row we want.

Answer 2

Here's my array-functional spin on the task. It is not likely to be faster than @ArtisticPhoenix's solution, but it provides the desired output without loop constructs or conditions. ...just different for the sake of being different.

The process generates a full-sized array of strings that "looks" like a vertical stroke of asterisks, then replaces the middle element with a horizontal stroke element.

Code: (Demo)

$size = 7;                                                     // circumference not radius 
$vertical = str_pad('*', $size * 2 - 1, ' ', STR_PAD_BOTH);    // row w/ central symbol
$result = array_fill(0, $size, $vertical);                     // top-to-bottom stroke of symbols
$result[$size / 2] = implode(' ', array_fill(0, $size, '*'));  // left-to-right stroke of symbols
echo implode(PHP_EOL, $result);

For improved readability, I've declared the single-use variable $vertical.

Output: (highlight the text with your cursor to see that the pattern has no unnecessary trailing spaces in any line.)

      *      
      *      
      *      
* * * * * * *
      *      
      *      
      *      

*notice that I am not bothering to floor() the "horizontal stroke" element key, because php casts float keys to integers. https://www.php.net/manual/en/language.types.array.php