return all keys of nested array

Using RecursiveIteratorIterator

$array = array(
  1400 => array(
    7300 => array(
      7301=> array(),
      7302 => array(),
      7305 => array(
        7306=>array()
      ),
    ),
    7314=>array()
  ),
);

function getKeys($key, $array) {
  $found_path = [];
  $ritit = new RecursiveIteratorIterator(new RecursiveArrayIterator($array), RecursiveIteratorIterator::SELF_FIRST);

  foreach ($ritit as $leafValue) {

    $path = array();
    foreach (range(0, $ritit->getDepth()) as $depth) {
      $path[] = $ritit->getSubIterator($depth)->key();
    }

    if (end($path) == $key) {
      $found_path = $path;
      break;
    }
  }

  return $found_path;
}

print_r(getKeys(7305, $array));
// Array
// (
//     [0] => 1400
//     [1] => 7300
//     [2] => 7305
// )

This is very interesting problem you have so I tried to make a function that will echo your keys. If this is not good enough pls let me know I can improve code. Thanks.

<?php

$a = array(
            1400=> 
                array(7300=>
                        array(
                            7301=> array(),
                            7302=> array(),
                            7305=> array(
                                7306=>array()
                            ),
                        ),
                    7314=>array()
                ),
            );

$mykey = 7306;
$level = 0;
$result = array();
$resultarray = test($a,$mykey,$level,$result);

function test($array,$mykey,$level,$result){
    $level++;
    foreach($array as $key => $element){
        if($key == $mykey){
            echo 'found';
            print_r($result);
            exit;
        } else if(is_array($element)){
            $result[$level] = $key;
            $result1 = test($element,$mykey,$level,$result);
        }
    }
}

The idea is to check current array branch, and if the needle key isn't found, then iterate current items and check their array child nodes by recursive function calls. Before each step down we push a current key to stack, and pop the stack if the function does not found a needle key in whole branch. So if the key found, the function returns true by the chain, preserving successful keys in the stack.

function branchTraversing(& $branch, & $key_stack, $needle_key) {
  $found = false;
  if (!array_key_exists($needle_key, $branch)) {
    reset($branch);
    while (!$found && (list($key, $next_branch) = each($branch))) {
      if (is_array($next_branch)) {
        array_push($key_stack, $key);
        $found = branchTraversing($next_branch, $key_stack, $needle_key);
        if (!$found) {
          array_pop($key_stack);
        }
      }
    }
  } else {
    array_push($key_stack, $needle_key);
    $found = true;
  }

  return $found;
}

function getPath(& $array, $needle_key) {
  $path = [];
  branchTraversing($array, $path, $needle_key);
  return $path;
}

$test_keys = [1400, 7300, 7302, 7306, 7314, 666];

foreach ($test_keys as $search_key) {
  echo '<p>' . $search_key . ' => [ '
  . implode(', ', getPath($array, $search_key)) . ' ]</p>';
}