How to implement hierarchical tree expansion recursively in PHP

This article mainly introduces the relevant information of PHP recursive implementation of hierarchical tree expansion. Friends in need can refer to the

renderings:

Implementation code:

<?php 
  
$db = mysql_connect(&#39;localhost&#39;, &#39;root&#39;, &#39;root&#39;) or die(&#39;Can\&#39;t connect to database&#39;); 
mysql_select_db(&#39;test&#39;) or die(&#39;Can\&#39;t find database : test&#39;); 
$result = mysql_query(&#39;select id, fid, name from tree&#39;); 
while($arr = mysql_fetch_array($result)){ 
  $data[] = array( 
    &#39;id&#39; => $arr[&#39;id&#39;],  
    &#39;fid&#39; => $arr[&#39;fid&#39;], 
    &#39;name&#39; => $arr[&#39;name&#39;],  
  ); 
} 
  
// 将数据按照缩进简单排列 见图1 
function data2arr($tree, $rootId = 0, $level = 0) { 
  foreach($tree as $leaf) { 
    if($leaf[&#39;fid&#39;] == $rootId) { 
      echo str_repeat(&#39;    &#39;, $level) . $leaf[&#39;id&#39;] . &#39; &#39; . $leaf[&#39;name&#39;] . &#39;<br/>&#39;; 
      foreach($tree as $l) { 
        if($l[&#39;fid&#39;] == $leaf[&#39;id&#39;]) { 
          data2arr($tree, $leaf[&#39;id&#39;], $level + 1); 
          break; 
        } 
      } 
    } 
  } 
} 
  
data2arr($data); 
echo &#39;<br/>-----------------------------------------------------------------------<br/>&#39;; 
  
// 将数据按照所属关系封装 见图2 
function arr2tree($tree, $rootId = 0) { 
  $return = array(); 
  foreach($tree as $leaf) { 
    if($leaf[&#39;fid&#39;] == $rootId) { 
      foreach($tree as $subleaf) { 
        if($subleaf[&#39;fid&#39;] == $leaf[&#39;id&#39;]) { 
          $leaf[&#39;children&#39;] = arr2tree($tree, $leaf[&#39;id&#39;]); 
          break; 
        } 
      } 
      $return[] = $leaf; 
    } 
  } 
  return $return; 
} 
  
$tree = arr2tree($data); 
print_r($tree); 
echo &#39;<br/>-----------------------------------------------------------------------<br/>&#39;; 
  
// 将数据使用HTML再次展现 见图3 
function tree2html($tree) { 
  echo &#39;<ul>&#39;; 
  foreach($tree as $leaf) { 
    echo &#39;<li>&#39; .$leaf[&#39;name&#39;]; 
    if(! emptyempty($leaf[&#39;children&#39;])) tree2html($leaf[&#39;children&#39;]); 
    echo &#39;</li>&#39;; 
  } 
  echo &#39;</ul>&#39;; 
} 
  
tree2html($tree);

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