two_sum_iv.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


class Solution:
    def __init__(self):
        self.elements = set()

    def findTarget(self, root: TreeNode, k: int) -> bool:
        if root is None: return False
        if k - root.val in self.elements: return True
        self.elements.add(root.val)
        return self.findTarget(root.left, k) or self.findTarget(root.right, k)