LeetCode - Range Sum of BST

Given the root node of a binary search tree, return the sum of values of all nodes with a value in the range [low, high].

 

Example 1:


Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Example 2:


Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
 

Constraints:

The number of nodes in the tree is in the range [1, 2 * 104].
1 <= Node.val <= 105
1 <= low <= high <= 105
All Node.val are unique.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int sum = 0;
    public int rangeSumBST(TreeNode root, int low, int high) {    
        helper(root, low, high);
        return sum;
    }
    
    public void helper (TreeNode node, int low, int high) {
        if (node == null) {
            return;
        }
        if (node.val >= low && node.val <= high) {
            sum = sum + node.val;
            helper(node.left, low, high);
            helper(node.right, low, high);
        }
        else if (node.val > high) {
            helper(node.left, low, high);
        }
        else {
            helper(node.right, low, high);
        }
    }
}