本文主要介绍了php实现的二叉树遍历算法,结合具体实例形式分析了php针对二叉树的常用前序、中序及后序遍历算法实现技巧,需要的朋友可以参考一下!想了解更多相关信息请持续关注我们应届毕业生考试网!

<?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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