算法1

(递归) $O(n)$

最简洁

C++ 代码

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