938_rangesumofBST.cpp

//  * Definition for a binary tree node.
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() : val(0), left(nullptr), right(nullptr) {}
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

class Solution {
public:
    int rangeSumBST(TreeNode* root, int low, int high) {
        if (root == nullptr) {
            return 0;
        }
        
        if (root->val < low) {
            return rangeSumBST(root->right, low, high);
        }
        
        if (root->val > high) {
            return rangeSumBST(root->left, low, high);
        }
        
        return root->val + rangeSumBST(root->left, low, high) + rangeSumBST(root->right, low, high);
    }
};