/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
struct TreeNode* mirrorTree(struct TreeNode* root){
if(root==NULL)
return NULL;
struct TreeNode *tmp;
tmp=root->left;
root->left=root->right;
root->right=tmp;
mirrorTree(root->left);
mirrorTree(root->right);
return root;
}