0938-Range Sum of BST.md

Range Sum of BST

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

Example 2:

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

Note:

1. The number of nodes in the tree is at most 10000.
2. The final answer is guaranteed to be less than 2^31.

Solution

O(log[base 2](n)) Time - Recursive:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func rangeSumBST(_ root: TreeNode?, _ L: Int, _ R: Int) -> Int {
        guard let node = root else { return 0 }
        switch node.val {
            case Int.min..<L:
            return rangeSumBST(node.right, L, R)
            case R+1...Int.max:
            return rangeSumBST(node.left, L, R)
            default:
            return node.val + rangeSumBST(node.left, L, R) + rangeSumBST(node.right, L, R)
        }
    }
}