653. Two Sum IV - Input is a BST
Đề Bài
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 <= 104rootis guaranteed to be a valid binary search tree.-105 <= k <= 105
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(n)
💾 Không gian
O(n)
Lời Giải
Python
0653-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 __init__(self):
self.check = False
self.hashSet = set()
def LNR(self, root, k):
if not root or self.check:
return
self.LNR(root.left, k)
if root.val in self.hashSet:
self.check = True
self.hashSet.add(k - root.val)
self.LNR(root.right, k)
def findTarget(self, root: Optional[TreeNode], k: int) -> bool:
self.LNR(root, k)
return self.check