1261. Find Elements in a Contaminated Binary Tree**
https://leetcode.com/problems/find-elements-in-a-contaminated-binary-tree/
题目描述
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 True
Example 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 False
Example 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 True
Constraints:
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
C++ 实现 1
本题是说, 一棵二叉树原本满足一开始的三个条件, 但是现在收到了污染, 所有节点的值都变成了 -1, 因此需要先编写方法恢复出原来的二叉树, 然后在恢复出来的二叉树中查找指定元素. 可以采用哈希表保存元素, 查找元素就非常方便. 而恢复二叉树的工作, 可以使用前序遍历.
class FindElements {
private:
unordered_set<int> record;
void recover(TreeNode *root) {
if (!root) return;
if (root->left) {
root->left->val = 2 * root->val + 1;
record.insert(root->left->val);
}
if (root->right) {
root->right->val = 2 * root->val + 2;
record.insert(root->right->val);
}
recover(root->left);
recover(root->right);
}
public:
FindElements(TreeNode* root) {
if (root) {
root->val = 0;
record.insert(root->val);
recover(root);
}
}
bool find(int target) {
return record.count(target);
}
};
/**
* Your FindElements object will be instantiated and called as such:
* FindElements* obj = new FindElements(root);
* bool param_1 = obj->find(target);
*/