C++ Super-Simple and Easy Recursive Solution
We iterate through the entire tree.\nFor every node, if its value is within the range, we add it to res.\n\nclass Solution {\npublic:\n    void rec(TreeNode* ro
We iterate through the entire tree.\nFor every node, if its value is within the range, we add it to `res`.\n```\nclass Solution {\npublic:\n    void rec(TreeNode* root, int low, int high) {\n        if (!root) return;\n        if (root->val <= high && root->val >= low) res += root->val;\n        rec(root->left, low, high);\n        rec(root->right, low, high);\n    }\n    \n    int rangeSumBST(TreeNode* root, int low, int high) {\n        rec(root, low, high);\n        return res;\n    }\n    \nprivate:\n    int res = 0;\n};\n```
['C']