在递归调用中使用引用时遇到问题。
我所要做的是根据一个元素中不同节点的最大数量来描述一个XML文档，而不预先知道任何节点元素的名称。
考虑本文件：

<Data>
    <Record>
        <SAMPLE>
            <TITLE>Superior Title</TITLE>
            <SUBTITLE>Sub Title</SUBTITLE>
            <AUTH>
                <FNAME>John</FNAME>
                <DISPLAY>No</DISPLAY>
            </AUTH>
            <AUTH>
                <FNAME>Jane</FNAME>
                <DISPLAY>No</DISPLAY>
            </AUTH>
            <ABSTRACT/>
        </SAMPLE>
    </Record>
    <Record>
        <SAMPLE>
            <TITLE>Interesting Title</TITLE>
            <AUTH>
                <FNAME>John</FNAME>
                <DISPLAY>No</DISPLAY>
            </AUTH>
            <ABSTRACT/>
        </SAMPLE>
        <SAMPLE>
            <TITLE>Another Title</TITLE>
            <AUTH>
                <FNAME>Jane</FNAME>
                <DISPLAY>No</DISPLAY>
            </AUTH>
            <ABSTRACT/>
        </SAMPLE>
    </Record>
</Data>

$result = [

  "Data" => [
    "max_count" => 1,
    "elements" => [

      "Record" => [
        "max_count" => 2,
        "elements" => [

          "SAMPLE" => [
            "max_count" => 2,
            "elements" => [

              "TITLE" => [
                "max_count" => 1
              ],
              "SUBTITLE" => [
                "max_count" => 1
              ],
              "AUTH" => [
                "max_count" => 2,
                "elements" => [

                  "FNAME" => [
                    "max_count" => 1
                  ],
                  "DISPLAY" => [
                    "max_count" => 1
                  ]

                ]
              ],
              "ABSTRACT" => [
                "max_count" => 1
              ]

            ]
          ]

        ]
      ]

    ]
  ]

];

  private function countArrayElements(&$array, &$result){
    // get collection of subnodes
    foreach ($array as $node){

      $name = $this->stripNamespace($node['name']);

      // get count of distinct subnodes
      if (empty($result[$name])){
        $result[$name]["max_count"] = 1;
      } else {
        $result[$name]["max_count"]++;
      }

      if (is_array($node['value'])){
        $this->countArrayElements($node['value'], $result[$name]["elements"]);
      }

    }
  }

  private function countArrayElements(&$array, &$previous){

    // get collection of subnodes
    foreach ($array as $node){

      $name = $this->stripNamespace($node['name']);

      // get count of distinct subnodes
      if (empty($result[$name]["max_count"])){
        $result[$name]["max_count"] = 1;
      } else {
        $result[$name]["max_count"]++;
      }

      // recurse
      if (is_array($node['value'])){
        $result[$name]["elements"] = $this->countArrayElements(
          $node['value'],
          $result[$name]["elements"]
        );
      }

      // compare previous max
      if (!empty($previous[$name]["max_count"])){
        $result[$name]["max_count"] = max(
          $previous[$name]["max_count"],
          $result[$name]["max_count"]
        );
      }

    }

    return $result;

  }

最佳答案

虽然您的解决方案工作正常，而且考虑到它在O(n*k)时间内运行（其中n是树中的节点数，k是顶点数），但我想我会提出一个替代解决方案，它不依赖数组或引用，而且更通用，而不仅仅是工作对于xml，但是对于任何dom树。这个解决方案也可以在O(n*k)时间内运行，所以它同样有效。唯一的区别是您可以使用generator中的值，而不必首先构建整个数组。
建立问题模型
对我来说，理解这个问题最简单的方法就是把它建模为一个图。如果我们用这种方法对文档建模，我们得到的是级别和顶点。

因此，有效地，这使我们能够分而治之，将问题分解为两个不同的步骤。
将给定垂直节点的基数子节点名计算为sum（垂直）
在水平面（水平面）上找到集合的max。
这意味着，如果我们在此树上执行级别顺序遍历，我们应该能够轻松地生成节点名称的基数作为所有垂直节点的最大和。

换句话说，获取每个节点的不同子节点名是一个基数问题。然后是找到整个水平的最大和的问题。
最小、完整、可验证、自包含的示例
因此，为了提供一个最小、完整、可验证和自包含的示例，我将依赖于扩展php的sum，而不是您在示例中使用的第三方xml库。
可能值得注意的是，这段代码与php 5不向后兼容（因为使用了DOMDocument），因此必须使用php 7才能使此实现正常工作。
首先，我将在yield from中实现一个函数，它允许我们使用generator按级别顺序遍历dom树。

class SpecialDOM extends DOMDocument {
    public function level(DOMNode $node = null, $level = 0, $ignore = ["#text"]) {
        if (!$node) {
            $node = $this;
        }
        $stack = [];
        if ($node->hasChildNodes()) {
            foreach($node->childNodes as $child) {
                if (!in_array($child->nodeName, $ignore, true)) {
                    $stack[] = $child;
                }
            }
        }
        if ($stack) {
            yield $level => $stack;
            foreach($stack as $node) {
                yield from $this->level($node, $level + 1, $ignore);
            }
        }
    }
}

$xml = <<<'XML'
<?xml version="1.0" encoding="UTF-8"?>

<Data>
    <Record>
        <SAMPLE>Some Sample</SAMPLE>
    </Record>
    <Note>
        <SAMPLE>Some Sample</SAMPLE>
    </Note>
    <Record>
        <SAMPLE>Sample 1</SAMPLE>
        <SAMPLE>Sample 2</SAMPLE>
    </Record>
</Data>
XML;

$dom = new SpecialDOM;
$dom->loadXML($xml);

foreach($dom->level() as $level => $stack) {
    echo "- Level $level\n";
    foreach($stack as $item => $node) {
        echo "$item => $node->nodeName\n";
    }
}

- Level 0
0 => Data
- Level 1
0 => Record
1 => Note
2 => Record
- Level 2
0 => SAMPLE
- Level 2
0 => SAMPLE
- Level 2
0 => SAMPLE
1 => SAMPLE

So at least now we have a way of knowing what level a node is on and in what order it appears on that level, which is useful for what we intend to do.

Now the idea of building a nested array is actually unnecessary to obtain the cardinality sought by max_count. Because we already have access to the nodes themselves from the DOM tree. Which means we know what elements are contained therein inside of our loop at each iteration. We don't have to generate the entire array at once to begin exploring it. We can do this at a level-order instead, which is actually really cool, because it means you can build a flat array to get to max_count for each record.

Let me demonstrate how that would work.

$max = [];
foreach($dom->level() as $level => $stack) {
    $sum = [];
    foreach($stack as $item => $node) {
        $name = $node->nodeName;
        // the sum
        if (!isset($sum[$name])) {
            $sum[$name] = 1;
        } else {
            $sum[$name]++;
        }
        // the maximum
        if (!isset($max[$level][$name])) {
            $max[$level][$name] = 1;
        } else {
            $max[$level][$name] = max($sum[$name], $max[$level][$name]);
        }
    }
}

var_dump($max);

关于php - 如何获得不同XML节点的数量？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39260573/