LeetCode 101. Symmetric Tree

代码：

class Solution {public:    bool isSymmetric(TreeNode *root)     {     if (root == NULL)     {     return true;     } else     {     return gao(root->left, root->right);     }    }private:bool gao(TreeNode *left, TreeNode *right){if (left!=NULL && right!=NULL){return left->val == right->val&& gao(left->left, right->right)&& gao(left->right, right->left);} else if (left==NULL && right==NULL){return true;} else{return false;}}};