//*** 递归 **//
void MirrorRecursively(TreeNode *pRoot)
{
    if((pRoot == NULL) || (pRoot->left == NULL && pRoot->right == NULL))
        return;

    TreeNode *pTemp = pRoot->left;
    pRoot->left = pRoot->right;
    pRoot->right = pTemp;
    
    if(pRoot->left)
        MirrorRecursively(pRoot->left);  

    if(pRoot->right)
        MirrorRecursively(pRoot->right); 
}


//*** 非递归 **//
void MirrorIteratively(TreeNode* pRoot)
{
    if(pRoot == NULL)
        return;

    std::stack<TreeNode*> stackTreeNode;
    stackTreeNode.push(pRoot);

    while(stackTreeNode.size() > 0)
    {
        TreeNode *pNode = stackTreeNode.top();
        stackTreeNode.pop();

        TreeNode *pTemp = pNode->left;
        pNode->left = pNode->right;
        pNode->right = pTemp;

        if(pNode->left)
            stackTreeNode.push(pNode->left);

        if(pNode->right)
            stackTreeNode.push(pNode->right);
    }
}