Detailed explanation of threaded binary trees and binary tree traversal methods implemented in PHP Threaded binary trees Preorder threaded binary trees Preorder threaded binary trees

The example in this article describes the clue binary tree and binary tree traversal method implemented in PHP. Share it with everyone for your reference, the details are as follows:

<&#63;php
  require 'biTree.php';
  $str = 'ko#be8#tr####acy#####';
  $tree = new BiTree($str);
  $tree->createThreadTree();
  echo $tree->threadList() . "\n";从第一个结点开始遍历线索二叉树
  echo $tree->threadListReserv();从最后一个结点开始反向遍历
?>

biTree.php:

<&#63;
  /**
   * PHP实现二叉树
   *
   * @author zhaojiangwei
   * @since 2011/10/25 10:32
   */
  //结点类
  class Node{
    private $data = NULL;
    private $left = NULL;
    private $right = NULL;
    private $lTag = 0;
    private $rTag = 0;
    public function Node($data = false){
      $this->data = $data;
    }
    //我不喜欢使用魔术方法
    public function getData(){
      return $this->data;
    }
    public function setData($data){
      $this->data = $data;
    }
    public function getLeft(){
      return $this->left;
    }
    public function setLeft($left){
      $this->left = $left;
    }
    public function getRight(){
      return $this->right;
    }
    public function setRight($right){
      $this->right = $right;
    }
    public function getLTag(){
      return $this->lTag;
    }
    public function setLTag($tag){
      $this->lTag = $tag;
    }
    public function getRTag(){
      return $this->rTag;
    }
    public function setRTag($tag){
      $this->rTag = $tag;
    }
  }
  //线索二叉树类
  class BiTree{
    private $datas = NULL;//要导入的字符串;
    private $root = NULL; //根结点
    private $leafCount = 0;//叶子结点个数
    private $headNode = NULL; //线索二叉树的头结点
    private $preNode = NULL;//遍历线索化二叉树时保存前一个遍历的结点
    public function BiTree($datas){
      is_array($datas) || $datas = str_split($datas);
      $this->datas = $datas;
      $this->backupData = $this->datas;
      $this->createTree(TRUE);
    }
    //前序遍历创建树
    //$root 判断是不是要创建根结点
    public function createTree($root = FALSE){
      if(emptyempty($this->datas)) return NULL;
      $first = array_shift($this->datas);
      if($first == '#'){
        return NULL;
      }else{
        $node = new Node($first);
        $root && $this->root = $node;
        $node->setLeft($this->createTree());
        $node->setRight($this->createTree());
        return $node;
      }
    }
    //返回二叉树叶子结点的个数
    public function getLeafCount(){
      $this->figureLeafCount($this->root);
      return $this->leafCount;
    }
    private function figureLeafCount($node){
      if($node == NULL)
        return false;
      if($this->checkEmpty($node)){
        $this->leafCount ++;
      }else{
        $this->figureLeafCount($node->getLeft());
        $this->figureLeafCount($node->getRight());
      }
    }
    //判断结点是不是叶子结点
    private function checkEmpty($node){
      if($node->getLeft() == NULL && $node->getRight() == NULL){
        return true;
      }
      return false;
    }
    //返回二叉树深度
    public function getDepth(){
      return $this->traversDepth($this->root);
    }
    //遍历求二叉树深度
    public function traversDepth($node){
      if($node == NULL){
        return 0;
      }
      $u = $this->traversDepth($node->getLeft()) + 1;
      $v = $this->traversDepth($node->getRight()) + 1;
      return $u > $v ? $u : $v;
    }
    //返回遍历结果,以字符串的形式
    //$order 按遍历形式返回,前中后
    public function getList($order = 'front'){
      if($this->root == NULL) return NULL;
      $nodeList = array();
      switch ($order){
        case "front":
          $this->frontList($this->root, $nodeList);
          break;
        case "middle":
          $this->middleList($this->root, $nodeList);
          break;
        case "last":
          $this->lastList($this->root, $nodeList);
          break;
        default:
          $this->frontList($this->root, $nodeList);
          break;
      }
      return implode($nodeList);
    }
    //创建线索二叉树
    public function createThreadTree(){
      $this->headNode = new Node();
      $this->preNode = & $this->headNode;
      $this->headNode->setLTag(0);
      $this->headNode->setLeft($this->root);
      $this->headNode->setRTag(1);
      $this->threadTraverse($this->root);
      $this->preNode->setRight($this->headNode);
      $this->preNode->setRTag(1);
      $this->headNode->setRight($this->preNode);
    }
    //线索化二叉树
    private function threadTraverse($node){
      if($node != NULL){
        if($node->getLeft() == NULL){
          $node->setLTag(1);
          $node->setLeft($this->preNode);
        }else{
          $this->threadTraverse($node->getLeft());
        }
        if($this->preNode != $this->headNode && $this->preNode->getRight() == NULL){
          $this->preNode->setRTag(1);
          $this->preNode->setRight($node);
        }
        $this->preNode = & $node;//注意传引用
        $this->threadTraverse($node->getRight());
      }
    }
    //从第一个结点遍历中序线索二叉树
    public function threadList(){
      $arr = array();
      for($node = $this->getFirstThreadNode($this->root); $node != $this->headNode; $node = $this->getNextNode($node)){
        $arr[] = $node->getData();
      }
      return implode($arr);
    }
    //从尾结点反向遍历中序线索二叉树
    public function threadListReserv(){
      $arr = array();
      for($node = $this->headNode->getRight(); $node != $this->headNode; $node = $this->getPreNode($node)){
        $arr[] = $node->getData();
      }
      return implode($arr);
    }
    //返回某个结点的前驱
    public function getPreNode($node){
      if($node->getLTag() == 1){
        return $node->getLeft();
      }else{
        return $this->getLastThreadNode($node->getLeft());
      }
    }
    //返回某个结点的后继
    public function getNextNode($node){
      if($node->getRTag() == 1){
        return $node->getRight();
      }else{
        return $this->getFirstThreadNode($node->getRight());
      }
    }
    //返回中序线索二叉树的第一个结点
    public function getFirstThreadNode($node){
      while($node->getLTag() == 0){
        $node = $node->getLeft();
      }
      return $node;
    }
    //返回中序线索二叉树的最后一个结点
    public function getLastThreadNode($node){
      while($node->getRTag() == 0){
        $node = $node->getRight();
      }
      return $node;
    }
    //前序遍历
    private function frontList($node, & $nodeList){
      if($node !== NULL){
        $nodeList[] = $node->getData();
        $this->frontList($node->getLeft(), $nodeList);
        $this->frontList($node->getRight(), $nodeList);
      }
    }
    //中序遍历
    private function middleList($node, & $nodeList){
      if($node != NULL){
        $this->middleList($node->getLeft(), $nodeList);
        $nodeList[] = $node->getData();
        $this->middleList($node->getRight(), $nodeList);
      }
    }
    //后序遍历
    private function lastList($node, & $nodeList){
      if($node != NULL){
        $this->lastList($node->getLeft(), $nodeList);
        $this->lastList($node->getRight(), $nodeList);
        $nodeList[] = $node->getData();
      }
    }
    public function getData(){
      return $this->data;
    }
    public function getRoot(){
      return $this->root;
    }
  }
?>

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