My 16ms C++ solution
\n    bool DFS(TreeNode *left,TreeNode *right)\n    {\n        if(left == NULL || right == NULL)\n            return left == right;\n        return (left->val =
    \n    bool DFS(TreeNode *left,TreeNode *right)\n    {\n        if(left == NULL || right == NULL)\n            return left == right;\n        return (left->val == right->val)&DFS(left->right,right->left)&DFS(left->left,right->right);\n    }\n    bool isSymmetric(TreeNode *root) {\n        if(root == NULL)\n            return true;\n        return DFS(root->left,root->right);\n    }
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