1 <?php
 2     class Node {
 3         public $data = null;
 4         public $parent = null;
 5         public $left = null;
 6         public $right = null;
 7     }
 8 
 9     #使用数组构造完全二叉树
10     function build_cbtree($a) {
11         $root = new Node();
12         $root->data = $a[0];
13 
14         for ($i = 1; $i < count($a); $i++) {
15             $node = new Node();
16             $node->data = $a[$i];
17             insert_node($root, $node);
18         }        
19 
20         return $root;
21     }
22 
23     #插入完全二叉树节点
24     function insert_node($root, $inode) {
25         #使用树的广度优先遍历顺序取出节点，直到找到第一个左右子节点没满的节点，将待插入节点插入节点左边或右边
26         $queue = array();
27         array_unshift($queue, $root);
28 
29         while (!empty($queue)) {
30             $cnode = array_pop($queue);
31             if ($cnode->left == null) {
32                 $cnode->left = $inode;
33                 $inode->parent = $cnode;
34                 return $root;
35             } else {
36                 array_unshift($queue, $cnode->left);                
37             }
38             if ($cnode->right == null) {
39                 $cnode->right = $inode;
40                 $inode->parent = $cnode;
41                 return $root;
42             } else {
43                 array_unshift($queue, $cnode->right);
44             }
45         }
46 
47         return $root;
48     }
49 
50     #树的广度优先遍历 
51     function bf_traverse($root) {
52         $queue = array();
53         array_unshift($queue, $root);
54 
55         while (!empty($queue)) {
56             $cnode = array_pop($queue);
57             echo $cnode->data . " ";
58             if ($cnode->left !== null) array_unshift($queue, $cnode->left);
59             if ($cnode->right !== null) array_unshift($queue, $cnode->right);
60         }
61 
62         echo "<br>";
63     }
64 
65     $a = array(9, 8, 7, 6, 8, 4, 3, 2, 1);
66     $root = build_cbtree($a);
67     bf_traverse($root); #广度优先遍历
68 ?>

9 8 7 6 8 4 3 2 1