[10/9] 653. Two Sum IV - Input is a BST

# 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 findTarget(self, root: Optional[TreeNode], k: int) -> bool:
        lookingfor = set()
        
        def dfs(node):
            if not node: return False
            if node.val in lookingfor:
                return True
                        
            lookingfor.add(k-node.val)
            
            return dfs(node.left) or dfs(node.right)
        
        
        return dfs(root)