Description
Given the root of a binary search tree and an integer k, return true if there exist two elements in the BST such that their sum is equal to k, or false otherwise.
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 <= 104rootis guaranteed to be a valid binary search tree.-105 <= k <= 105
Solution
Python3
# 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)