938. Range Sum of BST

Question 938

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

Answer

Iterative

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def rangeSumBST(self, root: TreeNode, L: int, R: int) -> int:
        ans = 0
        
        stack = [root]
        while stack:
            node = stack.pop()
            if node:
                if L <= node.val <= R:
                    ans += node.val
                if L < node.val:
                    stack.append( node.left )
                if R > node.val:
                    stack.append( node.right )
                    
        return ans

Recursive