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| <?php
* Class Node 節(jié)點
*/
class Node {
public $value;
public $left;
public $right;
public function __construct($value = null) {
$this->value = $value;
}
}
* Class BinaryTree 二叉樹
*/
class BinaryTree {
public $data;
public function __construct($data = []) {
$this->data = $data;
}
* 前序遍歷：
* 根節(jié)點 -> 左子樹 -> 右子樹
* 利用棧先進后出的特性，先訪問根節(jié)點，再把右子樹壓入，再壓入左子樹。
* 這樣取出的時候是先取出左子樹，最后取出右子樹。
*
* @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;
}
* 前序遍歷（遞歸）
*
* @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;
}
* 中序遍歷
* 左子樹 -> 根節(jié)點 -> 右子樹
* 需要從下向上遍歷，先把左子樹壓入棧，然后逐個訪問根節(jié)點和右子樹。
*
* @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;
}
* 中序遍歷（遞歸）
*
* @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;
}
* 后序遍歷
* 左子樹 -> 右子樹 -> 根節(jié)點
* 先把根節(jié)點存起來，然后依次儲存左子樹和右子樹。然后輸出。
*
* @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);
}
* 后序遍歷（遞歸）
*
* @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;
}
* 前序生成二叉樹
*
* @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);
|
