Most frequently asked interview question #13 with solution

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).
The binary search tree is guaranteed to have unique values.

Example 1:

Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32 

Solution in C++:

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

    int rangeSumBST(TreeNode* root, int L, int R) {
            int sum = 0;
        return cal_sum(root, L, R, sum);
    }
    int cal_sum (TreeNode* root, int L, int R, int &sum){
        if(!root){
            return 0;
        }
        if(root->left){
            cal_sum(root->left, L, R, sum);
        }
        if(root->right){
            cal_sum(root->right, L, R, sum);
        }
        if(root->val >= L && root->val <= R){
            sum += root->val;
        }
        return sum;
    }