[Leetcode] Binary tree--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

 Solution:

 

#traverse the tree and using's hash to store visited node
dic = {}
def helperRecursive(root):
if root is None:
return False
if (k - root.val) in dic:
return True
if root.val not in dic:
dic[root.val] = 1
return helperRecursive(root.left) or helperRecursive(root.right)

return helperRecursive(root)