LeetCode 653 Two Sum IV - Input is a BST 解题报告

题目要求

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.

题目分析及思路

给定一个二叉搜索树和一个目标值，若该树中存在两个元素的和等于目标值则返回true。可以先获得树中所有结点的值列表，然后遍历每个值，判断目标值与该值的差是否也在该列表中，并保存每个值的判断结果。若有一个true则返回true。

python代码

# Definition for a binary tree node.

# class TreeNode:

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution:

def findTarget(self, root: TreeNode, k: int) -> bool:

vals = []

q = collections.deque()

q.append(root)

while q:

size = len(q)

for _ in range(size):

node = q.popleft()

if not node:

continue

vals.append(node.val)

q.append(node.left)

q.append(node.right)

ans = []

for v in vals:

if k-v in vals and k-v != v:

ans.append(True)

else:

ans.append(False)

if True in ans:

return True

else:

return False