二叉树反转

invert a binary tree.

     4
   /     2     7
 / \   / 1   3 6   9

to

     4
   /     7     2
 / \   / 9   6 3   1

递归代码1：

TreeNode* invertTree(TreeNode* root) {
	if(root==NULL)
			return ;
		if ( root->left != NULL) invertTree(root->left);
                if ( root->right != NULL) invertTree(root->right);
		TreeNode * ptmpNode = root->left;
                root->left = root-right ;
                root->right = ptmpNode ;
    }

　递归代码2：

   TreeNode* invertTree(TreeNode* root) {
	if(root==NULL)
			return NULL;
		TreeNode * ptmpNode = root->left;
		root->left = invertTree(root->right);
		root->right = invertTree(ptmpNode);
		return root;
    }