php实现的二叉树遍历算法示例

本文实例讲述了php实现的二叉树遍历算法。分享给大家供大家参考，具体如下：

今天使用php来实现二叉树的遍历

创建的二叉树如下图所示

php代码如下所示：

<?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 $center_node->value . ' ';
      //先把右子树节点入栈，以确保左子树节点先出栈
      if($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 . ' ';
      $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 . ' ';
    }
  }
}
//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 = 'a';
$b->value = 'b';
$c->value = 'c';
$d->value = 'd';
$e->value = 'e';
$f->value = 'f';
$g->value = 'g';
$h->value = 'h';
$i->value = 'i';
$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 '<br/>';
//中序遍历
ergodic::midorder($a); //结果是： h d i b g a e c f
echo '<br/>';
//后序遍历
ergodic::endorder($a); //结果是: h i d g b e f c a

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希望本文所述对大家php程序设计有所帮助。