Two Sum IV - Input is a BST

#leetcode #dsa #theabbie

Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

Example 1:

Input: root = [5,3,6,2,4,null,7], k = 9
Output: true

Example 2:

Input: root = [5,3,6,2,4,null,7], k = 28
Output: false

Constraints:

The number of nodes in the tree is in the range [1, 104].
-104 <= Node.val <= 104
root is guaranteed to be a valid binary search tree.
-105 <= k <= 105

SOLUTION:

# 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 inorder(self, root, k):
        if root and not self.possible:
            self.inorder(root.left, k)
            if (k - root.val) in self.exists:
                self.possible = True
            self.exists.add(root.val)
            self.inorder(root.right, k)

    def findTarget(self, root: Optional[TreeNode], k: int) -> bool:
        self.possible = False
        self.exists = set()
        self.inorder(root, k)
        return self.possible