1 <?php
 2      #二叉树的广度优先遍历
 3      #使用一个队列实现
 4  
 5      class Node {
 6          public $data = null;
 7          public $left = null;
 8          public $right = null;
 9      }
10  
11      #@param $btree 二叉树根节点
12      function breadth_first_traverse($btree) {
13          $traverse_data = array();
14          $queue = array();
15          array_unshift($queue, $btree); #根节点入队
16          
17          while (!empty($queue)) { #持续输出节点，直到队列为空
18              $cnode = array_pop($queue); #队尾元素出队
19              $traverse_data[] = $cnode->data;
20  
21              #左节点先入队，然后右节点入队
22              if ($cnode->left != null) array_unshift($queue, $cnode->left);
23              if ($cnode->right != null) array_unshift($queue, $cnode->right);
24          }
25  
26          return $traverse_data;
27      }
28 
29      #深度优先遍历,使用一个栈实现
30      function depth_first_traverse($btree) {
31         $traverse_data = array();
32         $stack = array();
33         array_push($stack, $btree);
34 
35         while (!empty($stack)) {
36             $cnode = array_pop($stack);
37             $traverse_data[] = $cnode->data;
38 
39             if ($cnode->right != null) array_push($stack, $cnode->right);
40             if ($cnode->left != null) array_push($stack, $cnode->left);
41         }
42 
43         return $traverse_data;
44      }
45  
46      $root = new Node();
47      $node1 = new Node();
48      $node2 = new Node();
49      $node3 = new Node();
50      $node4 = new Node();
51      $node5 = new Node();
52      $node6 = new Node();
53  
54      $root->data = 1;
55      $node1->data = 2;
56      $node2->data = 3;
57      $node3->data = 4;
58      $node4->data = 5;
59      $node5->data = 6;
60      $node6->data = 7;
61  
62      $root->left = $node1;
63      $root->right = $node2;
64      $node1->left = $node3;
65      $node1->right = $node4;
66      $node2->left = $node5;
67      $node2->right = $node6;
68  
69      $traverse = breadth_first_traverse($root);
70      print_r($traverse);
71      echo "<br>";
72      $traverse = depth_first_traverse($root);
73      print_r($traverse);
74  ?>