(LEETCODSymmetric_tree.cpp

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        return root==NULL || isSymmetricHelp(root->left, root->right);
}


    bool isSymmetricHelp(TreeNode* left, TreeNode* right){
    if(left==NULL || right==NULL)
        return left==right;
    if(left->val!=right->val)
        return false;
    return isSymmetricHelp(left->left, right->right) && isSymmetricHelp(left->right, right->left);
    }
};