https://leetcode.com/problems/two-sum-iv-input-is-a-bst/

two_sum_buggy.py

# 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

def inorder(root):
    if root.left is not None:
        inorder(root.left)
    yield root
    if root.right:
        inorder(root.right)

def rev_inorder(root):
    if root.right:
        rev_inorder(root.right)
    yield root
    if root.left:
        rev_inorder(root.left)

class Solution:
    def findTarget(self, root: TreeNode, k: int) -> bool:
        l, r = inorder(root), rev_inorder(root)
        lk = next(l)
        rk = next(r)
        while lk is not rk:
            sm = lk.val + rk.val
            if sm == k:
                return 1
            elif sm < k:
                lk = next(l)
            else:
                rk = next(r)
        return 0

two_sum_correct.py

# 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

def inorder(root):
    if root.left is not None:
        yield from inorder(root.left)
    yield root
    if root.right:
        yield from inorder(root.right)

def rev_inorder(root):
    if root.right:
        yield from rev_inorder(root.right)
    yield root
    if root.left:
        yield from rev_inorder(root.left)

class Solution:
    def findTarget(self, root: TreeNode, k: int) -> bool:
        l, r = inorder(root), rev_inorder(root)
        lk = next(l)
        rk = next(r)
        while lk is not rk:
            sm = lk.val + rk.val
            if sm == k:
                return 1
            elif sm < k:
                lk = next(l)
            else:
                rk = next(r)
        return 0