C++ Solution - 91% Faster - Recursion
\t/\n\t * Definition for a binary tree node.\n\t * struct TreeNode {\n\t *     int val;\n\t *     TreeNode left;\n\t *     TreeNode right;\n\t *     TreeNode() 
\t/**\n\t * Definition for a binary tree node.\n\t * struct TreeNode {\n\t *     int val;\n\t *     TreeNode *left;\n\t *     TreeNode *right;\n\t *     TreeNode() : val(0), left(nullptr), right(nullptr) {}\n\t *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}\n\t *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}\n\t * };\n\t */\n\tclass Solution {\n\tpublic:\n\t\tint sum=0;\n\t\tint rangeSumBST(TreeNode* root, int low, int high) {\n\t\t\tif(root==NULL){\n\t\t\t\treturn 0;\n\t\t\t}\n\t\t\tif(root->val >= low && root->val <= high){\n\t\t\t\tsum+=root->val;\n\t\t\t}\n\t\t\trangeSumBST(root->left,low,high);\n\t\t\trangeSumBST(root->right,low,high);\n\n\t\t\treturn sum;\n\n\n\t\t}\n\n\t};\n\t\n**\tPlease upvote if it helped. **
['Recursion', 'C']