Two Sum IV - Input is a BST(bfs+set)
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.
Example 1:
Input:
5
/ \
3 6
/ \ \
2 4 7
Target = 9
Output:
True
Example 2:
Input:
5
/ \
3 6
/ \ \
2 4 7
Target = 28
分析
two sum。一个queue存元素,一个set存值。bfs 每次检查k-root.val是否在set里
class Solution:
def findTarget(self, root, k):
"""
:type root: TreeNode
:type k: int
:rtype: bool
"""
if not root:
return False
s = set()
q = collections.deque([root])
while q:
n = q.popleft()
if n:
if k - n.val in s:
return True
s.add(n.val)
q.append(n.left)
q.append(n.right)
return False
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