【leetcode】1261. Find Elements in a Contaminated Binary Tree
题目如下:
Given a binary tree with the following rules:
root.val == 0
- If
treeNode.val == x
andtreeNode.left != null
, thentreeNode.left.val == 2 * x + 1
- If
treeNode.val == x
andtreeNode.right != null
, thentreeNode.right.val == 2 * x + 2
Now the binary tree is contaminated, which means all
treeNode.val
have been changed to-1
.You need to first recover the binary tree and then implement the
FindElements
class:
FindElements(TreeNode* root)
Initializes the object with a contamined binary tree, you need to recover it first.bool find(int target)
Return if thetarget
value exists in the recovered binary tree.Example 1:
Input
["FindElements","find","find"]
[[[-1,null,-1]],[1],[2]]
Output
[null,false,true]
Explanation
FindElements findElements = new FindElements([-1,null,-1]);
findElements.find(1); // return False
findElements.find(2); // return TrueExample 2:
Input
["FindElements","find","find","find"]
[[[-1,-1,-1,-1,-1]],[1],[3],[5]]
Output
[null,true,true,false]
Explanation
FindElements findElements = new FindElements([-1,-1,-1,-1,-1]);
findElements.find(1); // return True
findElements.find(3); // return True
findElements.find(5); // return FalseExample 3:
Input
["FindElements","find","find","find","find"]
[[[-1,null,-1,-1,null,-1]],[2],[3],[4],[5]]
Output
[null,true,false,false,true]
Explanation
FindElements findElements = new FindElements([-1,null,-1,-1,null,-1]);
findElements.find(2); // return True
findElements.find(3); // return False
findElements.find(4); // return False
findElements.find(5); // return TrueConstraints:
TreeNode.val == -1
- The height of the binary tree is less than or equal to
20
- The total number of nodes is between
[1, 10^4]
- Total calls of
find()
is between[1, 10^4]
0 <= target <= 10^6
解题思路:题目很简单,先把树恢复,然后判断值是否存在。
代码如下:
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None class FindElements(object):
dic = {}
root = None
def __init__(self, root):
"""
:type root: TreeNode
"""
self.dic = {}
self.root = root
def recursive(node,node_val):
node.val = node_val
self.dic[node.val] = 1
if node.left != None:
recursive(node.left,node.val*2+1)
if node.right != None:
recursive(node.right,node.val*2+2)
recursive(self.root,0) def find(self, target):
"""
:type target: int
:rtype: bool
"""
return target in self.dic # Your FindElements object will be instantiated and called as such:
# obj = FindElements(root)
# param_1 = obj.find(target)
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