php编程--二叉树遍历算法实现

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：

1.  
   <?php
2.  
   class Node {
3.  
   public $value;
4.  
   public $child_left;
5.  
   public $child_right;
6.  
   }
7.  
   final class Ergodic {
8.  
   //前序遍历:先访问根节点，再遍历左子树，最后遍历右子树；并且在遍历左右子树时，仍需先遍历根节点，然后访问左子树，最后遍历右子树
9.  
   public static function preOrder($root){
10.  
    $stack = array();
11.  
    array_push($stack, $root);
12.  
    while(!empty($stack)){
13.  
    $center_node = array_pop($stack);
14.  
    echo $center_node->value . ' ';
15.  
     
16.  
    //先把右子树节点入栈，以确保左子树节点先出栈
17.  
    if($center_node->child_right != null) array_push($stack, $center_node->child_right);
18.  
    if($center_node->child_left != null) array_push($stack, $center_node->child_left);
19.  
    }
20.  
    }
21.  
    //中序遍历:先遍历左子树、然后访问根节点，最后遍历右子树；并且在遍历左右子树的时候。仍然是先遍历左子树，然后访问根节点，最后遍历右子树
22.  
    public static function midOrder($root){
23.  
    $stack = array();
24.  
    $center_node = $root;
25.  
    while (!empty($stack) || $center_node != null) {
26.  
    while ($center_node != null) {
27.  
    array_push($stack, $center_node);
28.  
    $center_node = $center_node->child_left;
29.  
    }
30.  
     
31.  
    $center_node = array_pop($stack);
32.  
    echo $center_node->value . ' ';
33.  
     
34.  
    $center_node = $center_node->child_right;
35.  
    }
36.  
    }
37.  
    //后序遍历:先遍历左子树，然后遍历右子树，最后访问根节点；同样，在遍历左右子树的时候同样要先遍历左子树，然后遍历右子树，最后访问根节点
38.  
    public static function endOrder($root){
39.  
    $push_stack = array();
40.  
    $visit_stack = array();
41.  
    array_push($push_stack, $root);
42.  
     
43.  
    while (!empty($push_stack)) {
44.  
    $center_node = array_pop($push_stack);
45.  
    array_push($visit_stack, $center_node);
46.  
    //左子树节点先入$pushstack的栈，确保在$visitstack中先出栈
47.  
    if ($center_node->child_left != null) array_push($push_stack, $center_node->child_left);
48.  
    if ($center_node->child_right != null) array_push($push_stack, $center_node->child_right);
49.  
    }
50.  
     
51.  
    while (!empty($visit_stack)) {
52.  
    $center_node = array_pop($visit_stack);
53.  
    echo $center_node->value . ' ';
54.  
    }
55.  
    }
56.  
    }
57.  
     
58.  
     
59.  
    //创建二叉树
60.  
    $a = new Node();
61.  
    $b = new Node();
62.  
    $c = new Node();
63.  
    $d = new Node();
64.  
    $e = new Node();
65.  
    $f = new Node();
66.  
    $g = new Node();
67.  
    $h = new Node();
68.  
    $i = new Node();
69.  
     
70.  
    $a->value = 'A';
71.  
    $b->value = 'B';
72.  
    $c->value = 'C';
73.  
    $d->value = 'D';
74.  
    $e->value = 'E';
75.  
    $f->value = 'F';
76.  
    $g->value = 'G';
77.  
    $h->value = 'H';
78.  
    $i->value = 'I';
79.  
     
80.  
    $a->child_left = $b;
81.  
    $a->child_right = $c;
82.  
    $b->child_left = $d;
83.  
    $b->child_right = $g;
84.  
    $c->child_left = $e;
85.  
    $c->child_right = $f;
86.  
    $d->child_left = $h;
87.  
    $d->child_right = $i;
88.  
     
89.  
     
90.  
    //前序遍历
91.  
    Ergodic::preOrder($a); //结果是：A B D H I G C E F
92.  
    echo '<br/>';
93.  
    //中序遍历
94.  
    Ergodic::midOrder($a); //结果是： H D I B G A E C F
95.  
    echo '<br/>';
96.  
    //后序遍历
97.  
    Ergodic::endOrder($a); //结果是: H I D G B E F C A