Find Elements in a Contaminated Binary Tree

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

class FindElements {
    TreeNode root;
    Set<Integer> set;

    public FindElements(TreeNode root) {
        this.root = root;
        set = new HashSet<>();
        fillTree(this.root, 0);
    }

    public void fillTree(TreeNode root, int val) {
        if (root == null)
            return;
        set.add(val);
        root.val = val;
        fillTree(root.left, 2 * val + 1);
        fillTree(root.right, 2 * val + 2);
    }

    public boolean find(int target) {
        return set.contains(target);
    }
}