PHP 实现二叉树的深度优先遍历

<?php
/*
 * 完成二叉树的深度优先遍历
 * 就是二叉树从根节点到叶子节点，是二叉树的先跟（先序）遍历
 * 递归与非递归解法
 * */
//二叉树的结构
class TreeNode{
    var $val;
    var $left = NULL;
    var $right = NULL;
    function __construct($val){
        $this->val = $val;
    }
}
//递归解法
function FindPath1($root)
{
    if(!empty($root)){
        echo $root->val;
        FindPath($root->left);
        FindPath($root->right);
    }else{
        return;
    }
}
//非递归解法
//使用栈来完成，先压右子树，再压左子树
function FindPath2($root)
{
    $arr = [];
    while(!empty($root)){
        echo $root->val;
        if(!empty($root->right)){
            array_push($arr,$root->right);
        }if(!empty($root->left)){
            array_push($arr,$root->left);
        }
        $root = array_pop($arr);
    }

}
//测试
$a = new TreeNode(1);
$b = new TreeNode(2);
$c = new TreeNode(3);
$d = new TreeNode(4);
$e = new TreeNode(5);
$f = new TreeNode(6);
$g = new TreeNode(7);
$h = new TreeNode(8);
$i = new TreeNode(9);
$j = new TreeNode(10);
$a->left = $b;
$a->right = $c;
$b->left = $d;
$b->right = $e;
$c->left = $f;
$c->right = $g;
$d->left = $h;
$d->right = $i;
$f->left = $j;
FindPath2($a);