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653. Two Sum IV - Input is a BST

Difficulty Topics

Description

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

two-sum-iv-input-is-a-bst.py
# 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 findTarget(self, root: Optional[TreeNode], k: int) -> bool:

        def dfs(root, curr):
            if not curr: return False

            return search(root, curr, k - curr.val) or dfs(root, curr.left) or dfs(root, curr.right)

        def search(root, curr, t):
            if not root: return False

            return (root.val == t and root.val != curr.val) or (root.val > t and search(root.left, curr, t)) or (root.val < t and search(root.right, curr, t))

        return dfs(root, root)