[Leetcode] Binary tree--653. Two Sum IV - Input is a BST
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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)
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