PHP Class&Object -- PHP实现二叉树

     二叉树及其变体是数据结构家族里的重要组成部分。最为链表的一种变体，二叉树最适合处理需要一特定次序快速组织和检索的数据。

    // 来自 PHP5 in Practice  (U.S.)Elliott III & Jonathan D.Eisenhamer

<?php// Define a class to implement a binary treeclass Binary_Tree_Node { // Define the variable to hold our data: public $data; // And a variable to hold the left and right objects: public $left; public $right; // A constructor method that allows for data to be passed in public function __construct($d = NULL) { $this->data = $d; } // Traverse the tree, left to right, in pre-order, returning an array // Preorder means that each node's value preceeds its children. public function traversePreorder() { // Prep some variables. $l = array(); $r = array(); // Read in the left and right children appropriately traversed: if ($this->left) { $l = $this->left->traversePreorder(); } if ($this->right) { $r = $this->right->traversePreorder(); } // Return a merged array of the current value, left, and right: return array_merge(array($this->data), $l, $r); } // Traverse the tree, left to right, in postorder, returning an array // Postorder means that each node's value follows its children. public function traversePostorder() { // Prep some variables. $l = array(); $r = array(); // Read in the left and right children appropriately traversed: if ($this->left) { $l = $this->left->traversePostorder(); } if ($this->right) { $r = $this->right->traversePostorder(); } // Return a merged array of the current value, left, and right: return array_merge($l, $r, array($this->data)); } // Traverse the tree, left to right, in-order, returning an array. // In-order means that values are ordered as left children, then the // node value, then the right children. public function traverseInorder() { // Prep some variables. $l = array(); $r = array(); // Read in the left and right children appropriately traversed: if ($this->left) { $l = $this->left->traverseInorder(); } if ($this->right) { $r = $this->right->traverseInorder(); } // Return a merged array of the current value, left, and right: return array_merge($l, array($this->data), $r); }}// Let's create a binary tree that will equal the following: 3// / / // h 9 // / / // Create the tree: 6 a $tree = new Binary_Tree_Node(3);$tree->left = new Binary_Tree_Node('h');$tree->right = new Binary_Tree_Node(9);$tree->right->left = new Binary_Tree_Node(6);$tree->right->right = new Binary_Tree_Node('a');// Now traverse this tree in all possible orders and display the results:// Pre-order: 3, h, 9, 6, aecho '<p>', implode(', ', $tree->traversePreorder()), '</p>';// Post-order: h, 9, 6, a, 3echo '<p>', implode(', ', $tree->traversePostorder()), '</p>';// In-order: h, 3, 6, 9, aecho '<p>', implode(', ', $tree->traverseInorder()), '</p>';?>