本文主要介紹了php實現的二叉樹遍歷演算法,結合具體例項形式分析了php針對二叉樹的常用前序、中序及後序遍歷演算法實現技巧,需要的朋友可以參考一下!想了解更多相關資訊請持續關注我們應屆畢業生考試網!
建立的二叉樹如下圖所示
php程式碼如下所示：
<?php
class Node {
public $value;
public $child_left;
public $child_right;
}
final class Ergodic {
//前序遍歷:先訪問根節點，再遍歷左子樹，最後遍歷右子樹；並且在遍歷左右子樹時，仍需先遍歷根節點，然後訪問左子樹，最後遍歷右子樹
public static function preOrder($root){
$stack = array();
array_push($stack, $root);
while(!empty($stack)){
$center_node = array_pop($stack);
echo $center_node->value . ' ';
//先把右子樹節點入棧，以確保左子樹節點先出棧
if($center_node->child_right != null) array_push($stack, $center_node->child_right);
if($center_node->child_left != null) array_push($stack, $center_node->child_left);
}
}
//中序遍歷:先遍歷左子樹、然後訪問根節點，最後遍歷右子樹；並且在遍歷左右子樹的`時候。仍然是先遍歷左子樹，然後訪問根節點，最後遍歷右子樹
public static function midOrder($root){
$stack = array();
$center_node = $root;
while (!empty($stack) || $center_node != null) {
while ($center_node != null) {
array_push($stack, $center_node);
$center_node = $center_node->child_left;
}
$center_node = array_pop($stack);
echo $center_node->value . ' ';
$center_node = $center_node->child_right;
}
}
//後序遍歷:先遍歷左子樹，然後遍歷右子樹，最後訪問根節點；同樣，在遍歷左右子樹的時候同樣要先遍歷左子樹，然後遍歷右子樹，最後訪問根節點
public static function endOrder($root){
$push_stack = array();
$visit_stack = array();
array_push($push_stack, $root);
while (!empty($push_stack)) {
$center_node = array_pop($push_stack);
array_push($visit_stack, $center_node);
//左子樹節點先入$pushstack的棧，確保在$visitstack中先出棧
if ($center_node->child_left != null) array_push($push_stack, $center_node->child_left);
if ($center_node->child_right != null) array_push($push_stack, $center_node->child_right);
}
while (!empty($visit_stack)) {
$center_node = array_pop($visit_stack);
echo $center_node->value . ' ';
}
}
}
//建立二叉樹
$a = new Node();
$b = new Node();
$c = new Node();
$d = new Node();
$e = new Node();
$f = new Node();
$g = new Node();
$h = new Node();
$i = new Node();
$a->value = 'A';
$b->value = 'B';
$c->value = 'C';
$d->value = 'D';
$e->value = 'E';
$f->value = 'F';
$g->value = 'G';
$h->value = 'H';
$i->value = 'I';
$a->child_left = $b;
$a->child_right = $c;
$b->child_left = $d;
$b->child_right = $g;
$c->child_left = $e;
$c->child_right = $f;
$d->child_left = $h;
$d->child_right = $i;
//前序遍歷
Ergodic::preOrder($a); //結果是：A B D H I G C E F
echo '<br/>';
//中序遍歷
Ergodic::midOrder($a); //結果是： H D I B G A E C F
echo '<br/>';
//後序遍歷
Ergodic::endOrder($a); //結果是: H I D G B E F C A
