二叉树的镜像

struct Tree()
{	
	int val;
	Tree *left, *right;
	Tree(int a): val(a), left(NULL), right(NULL){}
}
bool mirrorTree(Tree *root){
	
	if(root == NULL || (root->left== NULL && root->right == NULL)) return NULL ;
	 
	Tree *tp = root->left;
	root->left = root->right;
	root->right = tp;
	 
	if(root->left)
			mirrorTree(root->left);
	
	if(root->right)
			mirrorTree(root->right);
}