Tree Equalizer

gistfile1.php

<?php

$tree = array(
  'a' => array(
    'title' => 'The Big A',
    'children' => array(
      'a1' => array(
        'title' => 'The Lesser A1'
      ),
      'a2' => array(
        'title' => 'The Interesting A2'
      ),
    ),
  ),
  'b' => array(
    'title' => 'The Independent B'
  ),
  'c' => array(
    'title' => 'The Massive C',
    'children' => array(
      'c1' => array(
        'title' => 'The Cool C1',
        'children' => array(
          'c11' => array(
            'title' => 'The Awesome C11',
          ),
          'c12' => array(
            'title' => 'The Awesome C11',
          ),
          'c13' => array(
            'title' => 'The Awesome C11',
          ),
        ),
      ),
      'c2' => array(
        'title' => 'The Awesome C11',
      ),
    ),
  ),
);

// Execution
// ----------------------------------------------------------------------------
$depth = depth($tree);
$levels = array();
$table = deepen($tree, $depth, $levels);
$bottom = array_keys($levels[count($levels) - 1]);

print $depth . "\n";
print_r($table);
print_r($levels);
print_r($bottom);

// Helpers
// ----------------------------------------------------------------------------

/**
 * Recursively finds the max level in a given tree structure.
 */
function depth($branches, $depth = 0) {

  foreach($branches as $branch) {
    if (!empty($branch['children'])) {

      $detected = depth($branch['children'], $depth + 1);

      if ($detected > $depth) {
        $depth = $detected;
      }
    }
  }

  return $depth;
}

/**
 * Deepens the tree branches until all have the same depth with empty twigs.
 */
function deepen($branches, $max_level, &$levels = array(), $current_level = 0) {

  if ($current_level < $max_level) {
    foreach($branches as $key => &$branch) {

      $levels[$current_level][$key] = $branch;

      if (empty($branch['children'])) {
        $branch['children'] = array(
          $key => twig()
        );
      }

      $branch['children'] = deepen($branch['children'], $max_level, $levels, $current_level + 1);
    }
  }

  return $branches;
}

/**
 * An empty tree branch twig.
 */
function twig() {
  return array(
    'title' => ''
  );
}