Detailed explanation of binary tree traversal algorithm example code implemented in PHP

The so-called traversal refers to visiting each node in the tree once and only once along a certain search route. The operations performed to access the node depend on the specific application problem. Traversal is one of the most important operations on a binary tree and is the basis for other operations on a binary tree. This article mainly introduces the binary tree traversal algorithm implemented in PHP, and analyzes PHP's commonly used pre-order, in-order and post-order traversal algorithm implementation techniques for binary trees based on specific examples. Friends in need can refer to , as follows:

php codeis as follows:

<?php
class Node {
  public $value;
  public $child_left;
  public $child_right;
}
final class Ergodic {
  //前序遍历:先访问根节点，再遍历左子树，最后遍历右子树；并且在遍历左右子树时，仍需先遍历根节点，然后访问左子树，最后遍历右子树
  public static function preOrder($root){
    $stack = array();
    array_push($stack, $root);
    while(!empty($stack)){
      $center_node = array_pop($stack);
      echo $center_node->value . &#39; &#39;;
      //先把右子树节点入栈，以确保左子树节点先出栈
      if($center_node->child_right != null) array_push($stack, $center_node->child_right);
      if($center_node->child_left != null) array_push($stack, $center_node->child_left);
    }
  }
  //中序遍历:先遍历左子树、然后访问根节点，最后遍历右子树；并且在遍历左右子树的时候。仍然是先遍历左子树，然后访问根节点，最后遍历右子树
  public static function midOrder($root){
    $stack = array();
    $center_node = $root;
    while (!empty($stack) || $center_node != null) {
      while ($center_node != null) {
        array_push($stack, $center_node);
        $center_node = $center_node->child_left;
      }
      $center_node = array_pop($stack);
      echo $center_node->value . &#39; &#39;;
      $center_node = $center_node->child_right;
    }
  }
  //后序遍历:先遍历左子树，然后遍历右子树，最后访问根节点；同样，在遍历左右子树的时候同样要先遍历左子树，然后遍历右子树，最后访问根节点
  public static function endOrder($root){
    $push_stack = array();
    $visit_stack = array();
    array_push($push_stack, $root);
    while (!empty($push_stack)) {
      $center_node = array_pop($push_stack);
      array_push($visit_stack, $center_node);
      //左子树节点先入$pushstack的栈，确保在$visitstack中先出栈
      if ($center_node->child_left != null) array_push($push_stack, $center_node->child_left);
      if ($center_node->child_right != null) array_push($push_stack, $center_node->child_right);
    }
    while (!empty($visit_stack)) {
      $center_node = array_pop($visit_stack);
      echo $center_node->value . &#39; &#39;;
    }
  }
}
//创建二叉树
$a = new Node();
$b = new Node();
$c = new Node();
$d = new Node();
$e = new Node();
$f = new Node();
$g = new Node();
$h = new Node();
$i = new Node();
$a->value = &#39;A&#39;;
$b->value = &#39;B&#39;;
$c->value = &#39;C&#39;;
$d->value = &#39;D&#39;;
$e->value = &#39;E&#39;;
$f->value = &#39;F&#39;;
$g->value = &#39;G&#39;;
$h->value = &#39;H&#39;;
$i->value = &#39;I&#39;;
$a->child_left = $b;
$a->child_right = $c;
$b->child_left = $d;
$b->child_right = $g;
$c->child_left = $e;
$c->child_right = $f;
$d->child_left = $h;
$d->child_right = $i;
//前序遍历
Ergodic::preOrder($a); //结果是：A B D H I G C E F
echo &#39;<br/>&#39;;
//中序遍历
Ergodic::midOrder($a); //结果是： H D I B G A E C F
echo &#39;<br/>&#39;;
//后序遍历
Ergodic::endOrder($a); //结果是: H I D G B E F C A

The above is the detailed content of Detailed explanation of binary tree traversal algorithm example code implemented in PHP. For more information, please follow other related articles on the PHP Chinese website!