Pyramid Iteration

result.txt

         0
        101
       21012
      3210123
     432101234
    54321012345
   6543210123456
  765432101234567
 87654321012345678
9876543210123456789

                         A
                        BAB
                       CBABC
                      DCBABCD
                     EDCBABCDE
                    FEDCBABCDEF
                   GFEDCBABCDEFG
                  HGFEDCBABCDEFGH
                 IHGFEDCBABCDEFGHI
                JIHGFEDCBABCDEFGHIJ
               KJIHGFEDCBABCDEFGHIJK
              LKJIHGFEDCBABCDEFGHIJKL
             MLKJIHGFEDCBABCDEFGHIJKLM
            NMLKJIHGFEDCBABCDEFGHIJKLMN
           ONMLKJIHGFEDCBABCDEFGHIJKLMNO
          PONMLKJIHGFEDCBABCDEFGHIJKLMNOP
         QPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQ
        RQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQR
       SRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRS
      TSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRST
     UTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTU
    VUTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTUV
   WVUTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTUVW
  XWVUTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTUVWX
 YXWVUTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTUVWXY
ZYXWVUTSRQPONMLKJIHGFEDCBABCDEFGHIJKLMNOPQRSTUVWXYZ

test.php

<?php

version_compare(PHP_VERSION, '5.4.0', '>=') or die('Update your PHP Version, your version is no longer supported by php.net');

class PyramidIterator implements Iterator {
    
    private $range;
    private $row;
    
    public function __construct(array $range)
    {
        $this->range = $range;
        $this->rewind();
    }
    
    public function getIndentLength()
    {
        return count($this->range) - 1 - $this->row;
    }
    
    public function key()
    {
        return $this->row;
    }
    
    public function current()
    {
        $left = array_reverse(array_slice($this->range, 0 , $this->row + 1));
        $right = $this->key()
            ? array_slice($this->range, 1, $this->row)
            : [];
        
        return join($left).join($right);
    }
    
    public function next()
    {
        $this->row++;
    }
    
    public function valid()
    {
        return count($this->range) > $this->row;
    }
    
    public function rewind()
    {
        $this->row = 0;
    }
    
}

header('Content-Type: text/plain; charset=utf-8');

$content = [];
$iterator = new PyramidIterator(range(0,9));

foreach ( $iterator as $row ) {
    $content[] = str_repeat(' ', $iterator->getIndentLength()).$row;
}

echo join(PHP_EOL, $content);
    
echo PHP_EOL.PHP_EOL;

$content = [];
$iterator = new PyramidIterator(range('A', 'Z'));

foreach ( $iterator as $row ) {
    $content[] = str_repeat(' ', $iterator->getIndentLength()).$row;
}

echo join(PHP_EOL, $content);