1261. Find Elements in a Contaminated Binary Tree

1261. Find Elements in a Contaminated Binary Tree (Medium)

Given a binary tree with the following rules:

1. root.val == 0
2. If treeNode.val == x and treeNode.left != null, then treeNode.left.val == 2 * x + 1
3. If treeNode.val == x and treeNode.right != null, then treeNode.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 the target 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

Related Topics:
Hash Table, Tree

Solution 1.

// OJ: https://leetcode.com/problems/find-elements-in-a-contaminated-binary-tree/
// Author: github.com/lzl124631x
// Time:
//      FindElements: O(N)
//      find: O(1)
// Space: O(N)
class FindElements {
    unordered_set<int> s;
    void recover(TreeNode *root, int val) {
        if (!root) return;
        root->val = val;
        s.insert(val);
        recover(root->left, 2 * val + 1);
        recover(root->right, 2 * val + 2);
    }
public:
    FindElements(TreeNode* root) {
        recover(root, 0);
    }
    bool find(int target) {
        return s.count(target);
    }
};