// created by 曲朋維// 排序二叉樹// 完成以下任務.// 1. 將節點插入到對應位置// 2. 使用中序遍歷遍歷這個二叉樹// 3. 找到這個二叉樹的極值// 4. 搜索一個特定的值class Node{  public $key,$left,$right;  public function __construct($key)  {    $this->key = $key;  }}class BinaryTree{  public $root;  public $sortArr = [];  // 插入節點  public function insertNode($node,$newNode){    if ($node->key < $newNode->key){      // 如果父節點小于子節點,插到右邊      if (empty($node->right)){        $node->right = $newNode;      }else{        $this->insertNode($node->right,$newNode);      }    }elseif ($node->key > $newNode->key){      // 如果父節點大于子節點,插到左邊      if (empty($node->left)){        $node->left = $newNode;      }else{        $this->insertNode($node->left,$newNode);      }    }  }  public function insert($key){    $newNode = new Node($key);    if (empty($this->root)){      $this->root = $newNode;    }else{      $this->insertNode($this->root,$newNode);    }  }  // 中序遍歷  public function midSort(){    $this->midSortNode($this->root);  }  public function midSortNode($node){    if (!empty($node)){      $this->midSortNode($node->left);      array_push($this->sortArr,$node->key);      $this->midSortNode($node->right);    }  }  // 尋找極值  public function findMin(){    //不斷的找它的左子樹,直到這個左子樹的節點為葉子節點.    if (!empty($this->root)){      $this->findMinNode($this->root);    }  }  public function findMinNode(Node $node){    if (!empty($node->left)){      $this->findMinNode($node->left);    }else{      echo '這個二叉樹的最小值為:'.$node->key;    }  }  public function findMax(){    if (!empty($this->root)){      $this->findMaxNode($this->root);    }  }  public function findMaxNode(Node $node){    if (!empty($node->right)){      $this->findMaxNode($node->right);    }else{      echo '這個二叉樹的最大值為:'.$node->key;    }  }  // 查找特定的值  public function find($val = ''){    if (!empty($val)){      $this->findNode($this->root,$val);    }  }  public function findNode(Node $node,$val){    if ($node->key == $val){      echo '找到'.$val.'了';    }else if ($node->key > $val){      // 如果 父節點的值 大于要查找的值,那么查找它的左子樹      if (!empty($node->left)){        $this->findNode($node->left,$val);      }else{        echo '沒有這個東西!';      }    }else if ($node->key < $val){      if (!empty($node->right)){        $this->findNode($node->right,$val);      }else{        echo '沒有這個東西!';      }    }  }}$tree = new BinaryTree();// 節點插入$nodes = array(8,3,10,1,6,14,4,7,13);foreach ($nodes as $value){  $tree->insert($value);}// 中序遍歷//$tree->midSort();//print_r($tree->sortArr);// 尋找極值//$tree->findMin();//$tree->findMax();// 查找特定的值$tree->find(7);echo "<br/>";$tree->find(11);