27.二叉树的镜像

/**
 * 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;

}