653. Two Sum IV

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

思路：递归遍历BST（Binary Search Tree）

class Solution:
    def findTarget(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: bool
        """
        self.root = root
        self.k = k
        return self.searchNumber(root)
        
    def searchNumber(self, root):
        if not root:
            return False
        node = self.root
        n = self.k - root.val
        if n != root.val:
            while node:
                if node.val == n:
                    return True
                if n > node.val:
                    node = node.right
                else:
                    node = node.left
        return self.searchNumber(root.left) or self.searchNumber(root.right)