剑指Offer系列-面试题19：二叉树的镜像

题目：请完成一个函数，输入一个二叉树，该函数输出它的镜像。二叉树的结点定义如下：

struct BinaryTreeNode
{
    int m_nValue;
    BinaryTreeNode* m_pLeft;
    BinaryTreeNode* m_pRight;
};

思路：

代码：

// 递归实现
void MirrorRecursively(BinaryTreeNode *pNode)
{
    if((pNode == NULL) || (pNode->m_pLeft == NULL && pNode->m_pRight == NULL))
        return;

    BinaryTreeNode *pTemp = pNode->m_pLeft;
    pNode->m_pLeft = pNode->m_pRight;
    pNode->m_pRight = pTemp;

    if(pNode->m_pLeft)
        MirrorRecursively(pNode->m_pLeft);

    if(pNode->m_pRight)
        MirrorRecursively(pNode->m_pRight);
}

// 非递归实现
void MirrorIteratively(BinaryTreeNode* pRoot)
{
    if(pRoot == NULL)
        return;

    std::stack stackTreeNode;
    stackTreeNode.push(pRoot);

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

        BinaryTreeNode *pTemp = pNode->m_pLeft;
        pNode->m_pLeft = pNode->m_pRight;
        pNode->m_pRight = pTemp;

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

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