PHP反向递归

<code>// $formated_arr 是你的输入对象
// 首先按照level做一次排序
usort($formated_arr, function($a, $b) {
    $al = intval($a['level']);
    $bl = intval($b['level']);
    return ($al > $bl) ? 1 : -1;
});

// 因为上面做过排序了，所以这里虽然是递归，但对数组只遍历了一次
function reformat_tree(&$arrTmp, $parent_id=0) {
    $ret = null;
    foreach ($arrTmp as $k => $v) {
        if($v['parent_id'] == $parent_id) {
            $ret[$v['id']] = $v;
            unset($arrTmp[$k]);
            $child = reformat_tree($arrTmp, $v['id']);
            !is_null($child) ? $ret[$v['id']]['child'] = $child : 1;
        }
    }
    return $ret;
}

echo(json_encode(reformat_tree($formated_arr)));</code>

<code>function createMenuTree($data = array(), $pid = 0){
    if (empty($data)){
        return array();
    }
     static $level = 1;
     $returnArray = array();
    foreach ($data as $node){
        if ($node['parent_id'] == $pid){
            $returnArray[] = array(
                'cat_id'   => $node['cat_id'],
                'cat_name' => $node['cat_name'],
                'level' => $level,
                'parent_id' => $node['parent_id'],
                'show_in_nav' => $node['show_in_nav'],
                'is_show' => $node['is_show'],
                'sort_order' => $node['sort_order']
                );
            if (hasChild($node['cat_id'], $data)){
               $level++;
               $returnArray = array_merge($returnArray, createMenuTree($data, $node['cat_id']));
               $level--;
            }
        }
    }
     return $returnArray;
}

function hasChild($cid, $data){
    $hasChild = false;
    foreach ($data as $node){
        if ($node['parent_id'] == $cid){
            $hasChild = true;
            break;
        }
    }
    return $hasChild;
}
 </code>

<code>function recursive_tree($arr,$level = 0,$parent_id = 0){
    $tmp = array();       
    foreach ($arr as $key => $value) {
        if($value['level'] == $level && $value['parent_id'] == $parent_id){
            $arr[$key]['child'] = recursive_tree($arr,$value['level'] + 1,$value['id']);
            if(empty($arr[$key]['child'])){
                unset($arr[$key]['child']);
            }
            $tmp[] = $arr[$key];
        }
    }
    return $tmp;
}


$arr = array(
    array(
        'id'     => '125',
        'level' => '0',
        'user_id' => '1021',
        'parent_id' => '0', 
    ),
    array(
        'id'     => '189',
        'level' => '1',
        'user_id' => '1022',
        'parent_id' => '125', 
    ),
    array(
        'id'     => '425',
        'level' => '2',
        'user_id' => '4119',
        'parent_id' => '189', 
    ),
    array(
        'id'     => '385',
        'level' => '3',
        'user_id' => '3170',
        'parent_id' => '425', 
    ),
    array(
        'id'     => '782',
        'level' => '3',
        'user_id' => '5698',
        'parent_id' => '425', 
    ),
    array(
        'id'     => '688',
        'level' => '1',
        'user_id' => '7045',
        'parent_id' => '125', 
    )
);

echo json_encode(recursive_tree($arr,0,0));die;</code>