题干
请完成一个函数，输入一棵二叉树，该函数输出它的镜像。二叉树节点的定义如下：
class TreeNode{
int val;
TreeNode left;
TreeNode right;
}
解题思路
输入二叉树
graph TD
8-->6
8-->10
6-->5
6-->7
10-->9
10-->11
输出二叉树
graph TD
8-->10
8-->6
10-->11
10-->9
6-->7
6-->5
从图中可以分析出，输出的镜像二叉树和原二叉树的各个子树的根节点相同，子节点交换了位置，因为我们只需要将各个节点的左右孩子交换即可得到镜像。
代码实现
<?php
class TreeNode
{
private $val;
private $left;
private $right;
public function __set($name, $value)
{
$this->$name = $value;
}
public function __get($name)
{
return $this->$name;
}
}
function getTree()
{
$node1 = new TreeNode();
$node1->val = 8;
$node2 = new TreeNode();
$node2->val = 6;
$node3 = new TreeNode();
$node3->val = 10;
$node1->left = $node2;
$node1->right = $node3;
$node4 = new TreeNode();
$node4->val = 5;
$node5 = new TreeNode();
$node5->val = 7;
$node2->left = $node4;
$node2->right = $node5;
$node6 = new TreeNode();
$node6->val = 9;
$node7 = new TreeNode();
$node7->val = 11;
$node3->left = $node6;
$node3->right = $node7;
return $node1;
}
function mirror(&$tree)
{
if ($tree != null) {
$tmp = $tree->left;
$tree->left = $tree->right;
$tree->right = $tmp;
if ($tree->left!=null) {
mirror($tree->left);
}
if ($tree->right!=null){
mirror($tree->right);
}
}
}
$tree = getTree();
mirror($tree);
var_dump($tree);
