PHP构造二叉树算法示例

// 二叉树节点
class btnode {
  public $data;

  public $lchild = null;

  public $rchild = null;

  public function __construct($data) {
    $this->data = $data;
  }
}

function createbtnode(&$root,string $str)
{
  $strarr = str_split($str);
  $stack = [];
  $p = null; // 指针
  $top = -1;
  $k = $j = 0;
  $root = null;
  foreach ($strarr as $ch) {
    switch ($ch) {
      case '(':
        $top++;
        array_push($stack, $p);
        $k = 1;
        break;
      case ')':
        array_pop($stack);
        break;
      case ',':
        $k = 2;
        break;
      default:
        $p = new btnode($ch);
        if($root == null) {
          $root = $p;
        } else {
          switch ($k) {
            case 1:
              end($stack)->lchild = $p;
              break;
            case 2:
              end($stack)->rchild = $p;
              break;
          }
        }
        break;
    }
  }
}

function printbtnode($node)
{
  if($node != null) {
    printbtnode($node->lchild);
    echo $node->data;
    printbtnode($node->rchild);
  }
}