C++ | EASY SOLUTION
```\nclass FindElements {\npublic:\n    unordered_set set;\n    void recover(TreeNode root , int x){\n        if(!root ){\n            return ;\n        }\n    
```\nclass FindElements {\npublic:\n    unordered_set<int> set;\n    void recover(TreeNode* root , int x){\n        if(!root ){\n            return ;\n        }\n        set.insert(x);\n        recover(root->left , 2*x+1);\n        recover(root->right , 2*x+2);\n        \n    }\n    FindElements(TreeNode* root) {\n              recover(root, 0);\n\n    }\n\n    bool find(int target) {\n    return set.count(target);\n    }\n};
['Recursion', 'C']