938. Range Sum of BST

Problem

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

  Example 1:

Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 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.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} low
 * @param {number} high
 * @return {number}
 */
var rangeSumBST = function(root, low, high) {
    if (!root) return 0;
    if (root.val >= low && root.val <= high) {
        return root.val
            + rangeSumBST(root.left, low, high)
            + rangeSumBST(root.right, low, high);
    } else if (root.val < low) {
        return rangeSumBST(root.right, low, high);
    } else {
        return rangeSumBST(root.left, low, high);
    }
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(1).