递归方法非常简单：

1 void MirrorRecursively(BinaryTreeNode *pNode) 2 { 3     if((pNode == NULL) || (pNode->m_pLeft == NULL && pNode->m_pRight)) 4         return; 5  6     BinaryTreeNode *pTemp = pNode->m_pLeft; 7     pNode->m_pLeft = pNode->m_pRight; 8     pNode->m_pRight = pTemp; 9     10     if(pNode->m_pLeft)11         MirrorRecursively(pNode->m_pLeft);  12 13     if(pNode->m_pRight)14         MirrorRecursively(pNode->m_pRight); 15 }

循环需要利用stack：

1 void MirrorIteratively(BinaryTreeNode* pRoot) 2 { 3     if(pRoot == NULL) 4         return; 5  6     std::stack
     
       stackTreeNode; 7     stackTreeNode.push(pRoot); 8  9     while(stackTreeNode.size() > 0)10     {11         BinaryTreeNode *pNode = stackTreeNode.top();12         stackTreeNode.pop();13 14         BinaryTreeNode *pTemp = pNode->m_pLeft;15         pNode->m_pLeft = pNode->m_pRight;16         pNode->m_pRight = pTemp;17 18         if(pNode->m_pLeft)19             stackTreeNode.push(pNode->m_pLeft);20 21         if(pNode->m_pRight)22             stackTreeNode.push(pNode->m_pRight);23     }24 }