剑指offer---二叉树的镜像

递归版本：

struct TreeNode 
{
        int val;
        struct TreeNode *left;
        struct TreeNode *right;
        TreeNode(int x) :
        val(x), left(NULL), right(NULL) {}
};


class Solution 
{
public:
    void Mirror(TreeNode *pRoot) 
    {
        if(pRoot==NULL)
        {
            return;
        }
        
        //递归
        swap(pRoot->left,pRoot->right);
        Mirror(pRoot->left);
        Mirror(pRoot->right);
    }
};