Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 21

Description

Find Elements in a Contaminated Binary Tree

Given a binary tree with the following rules:

1. root.val == 0
2. For any treeNode:
   1. If treeNode.val has a value x and treeNode.left != null, then treeNode.left.val == 2 * x + 1
   2. If treeNode.val has a value 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.

Implement the FindElements class:

• FindElements(TreeNode* root) Initializes the object with a contaminated binary tree and recovers it.
• bool find(int target) Returns true 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, 104]
• Total calls of find() is between [1, 104]
• 0 <= target <= 106

Solution

class FindElements {
  set<int> nodes;
  void solve(TreeNode *root, int val) {
    if(!root) return;
    root->val = val;
    nodes.insert(val);
    solve(root->left, 2 * val + 1);
    solve(root->right, 2 * val + 2);
  }
public:
  FindElements(TreeNode* root) {
    solve(root, 0);
  }
  
  bool find(int target) {
    return nodes.count(target);
  }
};

// Accepted
// 31/31 cases passed (7 ms)
// Your runtime beats 82.43 % of cpp submissions
// Your memory usage beats 21.87 % of cpp submissions (34.9 MB)