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| <?php
* Class Node 节点
*/
class Node {
public $value;
public $left;
public $right;
public function __construct($value = null) {
$this->value = $value;
}
}
* Class BinaryTree 二叉树
*/
class BinaryTree {
public $data;
public function __construct($data = []) {
$this->data = $data;
}
* 前序遍历：
* 根节点 -> 左子树 -> 右子树
* 利用栈先进后出的特性，先访问根节点，再把右子树压入，再压入左子树。
* 这样取出的时候是先取出左子树，最后取出右子树。
*
* @param $tree
*
* @return array
*/
public function pre_order($tree) {
$stack = [];
$output = [];
array_push($stack, $tree);
while (!empty($stack)) {
$center_node = array_pop($stack);
$output[] = $center_node->value;
if ($center_node->right) {
array_push($stack, $center_node->right);
}
if ($center_node->left) {
array_push($stack, $center_node->left);
}
}
return $output;
}
* 前序遍历（递归）
*
* @param $tree
* @param $output
*
* @return array|void
*/
public function pre_order_recursive($tree, &$output) {
if (is_null($tree)) return; else {
$output[] = $tree->value;
$this->pre_order_recursive($tree->left, $output);
$this->pre_order_recursive($tree->right, $output);
}
return $output;
}
* 中序遍历
* 左子树 -> 根节点 -> 右子树
* 需要从下向上遍历，先把左子树压入栈，然后逐个访问根节点和右子树。
*
* @param $tree
*
* @return array
*/
public function in_order($tree) {
$stack = [];
$output = [];
$center_node = $tree;
while (!empty($stack) || $center_node != null) {
while ($center_node) {
array_push($stack, $center_node);
$center_node = $center_node->left;
}
$center_node = array_pop($stack);
if ($center_node->value) {
$output[] = $center_node->value;
}
$center_node = $center_node->right;
}
return $output;
}
* 中序遍历（递归）
*
* @param $tree
* @param $output
*
* @return array|void
*/
public function in_order_recursive($tree, &$output) {
if (is_null($tree)) return; else {
$this->in_order_recursive($tree->left, $output);
$output[] = $tree->value;
$this->in_order_recursive($tree->right, $output);
}
return $output;
}
* 后序遍历
* 左子树 -> 右子树 -> 根节点
* 先把根节点存起来，然后依次储存左子树和右子树。然后输出。
*
* @param $tree
*
* @return array
*/
public function tail_order($tree) {
$stack = [];
$output = [];
array_push($stack, $tree);
while (!empty($stack)) {
$center_node = array_pop($stack);
$output[] = $center_node->value;
if ($center_node->left) {
array_push($stack, $center_node->left);
}
if ($center_node->right) {
array_push($stack, $center_node->right);
}
}
return array_reverse($output);
}
* 后序遍历（递归）
*
* @param $tree
* @param $output
*
* @return array|void
*/
public function tail_order_recursive($tree, &$output) {
if (is_null($tree)) return; else {
$this->tail_order_recursive($tree->left, $output);
$this->tail_order_recursive($tree->right, $output);
$output[] = $tree->value;
}
return $output;
}
* 前序生成二叉树
*
* @param $root
*
* @return Node|string|void
*/
public function pre_order_create(&$root) {
$data = array_shift($this->data);
if (is_null($data)) return; elseif ($data == '#') return $root = null;
else {
$root = new Node($data);
$this->pre_order_create($root->left);
$this->pre_order_create($root->right);
}
return $root;
}
}
$data = array(0 => 'A',
1 => 'B',
2 => '#',
3 => 'D',
4 => '#',
5 => '#',
6 => 'C',
7 => '#',
8 => '#',);
$bt = new BinaryTree($data);
$tree = $bt->pre_order_create($root);
print_r($tree);
|
