Iterate/traverse BST Python

Question

I am trying to **find and sum ** all numbers in spesific range low - high in BST. I have accessed just the two numbers under the top of the tree. How to access all other numbers. When tried to iterate or traverse, I received errors.

`

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:

    def rangeSumBST(self, root: Optional[TreeNode], low: int, high: int) -> int:
        output = 0
        
        if  root.left.val >= low and root.left.val <= high:
            output += root.left.val
        if  root.right.val >= low and root.right.val <= high:
            output += root.right.val
        return output

`

Answer 1

As @nokla has said, you ideally want a recursive approach to this. Here's a variation on the recursive approach that's quite efficient:

class Solution:
    def rangeSumBST(self, root: Optional[TreeNode], low: int, high: int) -> int:
        _sum = 0
        def traverse(n):
            nonlocal _sum
            if n:
                if low <= n.val <= high:
                    _sum += n.val
                traverse(n.left)
                traverse(n.right)
        traverse(root)
        return _sum