<?php ob_start(); // Here we need to include the binary tree class Class Binary_Tree_Node() {    // You can find the details at } ob_end_clean(); // Define a class to implement self sorting binary tree class Sorting_Tree {     // Define the variable to hold our tree:     public $tree;     // We need a method that will allow for inserts that automatically place     // themselves in the proper order in the tree     public function insert($val) {         // Handle the first case:         if (!(isset($this->tree))) {             $this->tree = new Binary_Tree_Node($val);         } else {             // In all other cases:             // Start a pointer that looks at the current tree top:             $pointer = $this->tree;             // Iteratively search the tree for the right place:             for(;;) {                 // If this value is less than, or equal to the current data:                 if ($val <= $pointer->data) {                     // We are looking to the left ... If the child exists:                     if ($pointer->left) {                         // Traverse deeper:                         $pointer = $pointer->left;                     } else {                         // Found the new spot: insert the new element here:                         $pointer->left = new Binary_Tree_Node($val);                         break;                     }                 } else {                     // We are looking to the right ... If the child exists:                     if ($pointer->right) {                         // Traverse deeper:                         $pointer = $pointer->right;                     } else {                         // Found the new spot: insert the new element here:                         $pointer->right = new Binary_Tree_Node($val);                         break;                     }                 }             }         }     }     // Now create a method to return the sorted values of this tree.     // All it entails is using the in-order traversal, which will now     // give us the proper sorted order.     public function returnSorted() {         return $this->tree->traverseInorder();     } } // Declare a new sorting tree: $sort_as_you_go = new Sorting_Tree(); // Let's randomly create 20 numbers, inserting them as we go: for ($i = 0; $i < 20; $i++) {     $sort_as_you_go->insert(rand(1,100)); } // Now echo the tree out, using in-order traversal, and it will be sorted: // Example: 1, 2, 11, 18, 22, 26, 32, 32, 34, 43, 46, 47, 47, 53, 60, 71, //   75, 84, 86, 90 echo '<p>', implode(', ', $sort_as_you_go->returnSorted()), '</p>'; ?>