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Home Backend Development PHP Tutorial PHP implementation of binary tree traversal algorithm demonstration

PHP implementation of binary tree traversal algorithm demonstration

Jun 17, 2017 am 10:46 AM
php accomplish Demo algorithm Traverse

This article mainly introduces the binary tree traversal algorithm implemented by PHP, and analyzes PHP's commonly used pre-order, mid-order and post-order traversal algorithm implementation techniques for binary trees in the form of specific examples. Friends in need can refer to the following

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

Today I used php to implement binary tree traversal

The created binary tree is as shown below

php code is as follows:


<?php
class Node {
  public $value;
  public $child_left;
  public $child_right;
}
final class Ergodic {
  //前序遍歷:先訪問(wèn)根節(jié)點(diǎn),再遍歷左子樹(shù),最后遍歷右子樹(shù);并且在遍歷左右子樹(shù)時(shí),仍需先遍歷根節(jié)點(diǎn),然后訪問(wèn)左子樹(shù),最后遍歷右子樹(shù)
  public static function preOrder($root){
    $stack = array();
    array_push($stack, $root);
    while(!empty($stack)){
      $center_node = array_pop($stack);
      echo $center_node->value . &#39; &#39;;
      //先把右子樹(shù)節(jié)點(diǎn)入棧,以確保左子樹(shù)節(jié)點(diǎn)先出棧
      if($center_node->child_right != null) array_push($stack, $center_node->child_right);
      if($center_node->child_left != null) array_push($stack, $center_node->child_left);
    }
  }
  //中序遍歷:先遍歷左子樹(shù)、然后訪問(wèn)根節(jié)點(diǎn),最后遍歷右子樹(shù);并且在遍歷左右子樹(shù)的時(shí)候。仍然是先遍歷左子樹(shù),然后訪問(wèn)根節(jié)點(diǎn),最后遍歷右子樹(shù)
  public static function midOrder($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 = $center_node->child_right;
    }
  }
  //后序遍歷:先遍歷左子樹(shù),然后遍歷右子樹(shù),最后訪問(wèn)根節(jié)點(diǎn);同樣,在遍歷左右子樹(shù)的時(shí)候同樣要先遍歷左子樹(shù),然后遍歷右子樹(shù),最后訪問(wèn)根節(jié)點(diǎn)
  public static function endOrder($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, $center_node);
      //左子樹(shù)節(jié)點(diǎn)先入$pushstack的棧,確保在$visitstack中先出棧
      if ($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;;
    }
  }
}
//創(chuàng)建二叉樹(shù)
$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 = $i;
//前序遍歷
Ergodic::preOrder($a); //結(jié)果是:A B D H I G C E F
echo &#39;<br/>&#39;;
//中序遍歷
Ergodic::midOrder($a); //結(jié)果是: H D I B G A E C F
echo &#39;<br/>&#39;;
//后序遍歷
Ergodic::endOrder($a); //結(jié)果是: H I D G B E F C A

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