#
# [653] Two Sum IV - Input is a BST
#
# https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/
#
# algorithms
# Easy (49.94%)
# Total Accepted:    37.7K
# Total Submissions: 75.5K
# Testcase Example:  '[5,3,6,2,4,null,7]\n9'
#
# Given a Binary Search Tree and a target number, return true if there exist
# two elements in the BST such that their sum is equal to the given target.
# 
# Example 1:
# 
# Input: 
# ⁠   5
# ⁠  / \
# ⁠ 3   6
# ⁠/ \   \
# 2   4   7
# 
# Target = 9
# 
# Output: True
# 
# 
# 
# 
# Example 2:
# 
# Input: 
# ⁠   5
# ⁠  / \
# ⁠ 3   6
# ⁠/ \   \
# 2   4   7
# 
# Target = 28
# 
# Output: False
# 
# 
# 
# 
#
# 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
        """
        visited = set()
        return self.dfs(root,visited,k)
    
    def dfs(self, root, visited,k):
        if not root:
            return False
        
        if k - root.val in visited:
            return True
        visited.add(root.val)
        return self.dfs(root.right, visited,k) or self.dfs(root.left, visited,k)
        
