156. 上下翻转二叉树

题意：

解题思路：

思路：
1. 变换操作：左子树变成根节点，根节点变成右子树，右子树变成左子树；

PHP代码实现：

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($val = 0, $left = null, $right = null) {
 *         $this->val = $val;
 *         $this->left = $left;
 *         $this->right = $right;
 *     }
 * }
 */
class Solution {
    /**
     * @param TreeNode $root
     * @return TreeNode
     */
    function upsideDownBinaryTree($root) {
        if ($root == null || $root->left == null && $root->right == null) {
            return $root;
        }
        $node = $this->upsideDownBinaryTree($root->left);
        $root->left->left = $root->right;
        $root->left->right = $root;
        $root->left = null;
        $root->right = null;
        return $node;
    }
}

GO代码实现：

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func upsideDownBinaryTree(root *TreeNode) *TreeNode {
    if root == nil || root.Left == nil && root.Right == nil {
        return root
    }
    node := upsideDownBinaryTree(root.Left)
    root.Left.Left = root.Right
    root.Left.Right = root
    root.Left = nil
    root.Right = nil
    return node
}