two-sum-iv-input-is-a-bst

# link: https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def findTarget(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: bool
        """
        if not root: return False
        bfs, s = [root], set()
        for i in bfs:
            if k - i.val in s: return True
            s.add(i.val)
            if i.left: bfs.append(i.left)
            if i.right: bfs.append(i.right)
        return False