Problem1 Validate BST added

[megharaykar]

No description provided.

[super30admin]

Your solution is correct and follows the in-order traversal approach appropriately. Here are some strengths and areas for improvement:

Strengths:

• The code is clean and easy to understand.
• You have correctly identified the time and space complexity.
• The use of a helper function is good for encapsulating the recursion logic.
• The initialization of flag and prev in the __init__ method is correct, though note that for multiple test cases, this might cause issues if the same instance is reused. However, LeetCode typically creates a new instance per test case, so it should be safe.

Areas for Improvement:

• To improve efficiency, consider short-circuiting the recursion once a breach is detected. Currently, even after flag is set to False, the recursion continues through the entire tree. You can add a check to stop further recursion if flag is already False. For example, in the helper function, you could do:

  if not self.flag:
      return
  

  This will prevent unnecessary traversals after the first breach is found.
• Alternatively, you can return early without setting a flag by having the helper function return a boolean. However, the current approach is acceptable and similar to the reference solution.
• Note that in Python, using instance variables for flag and prev is acceptable, but be cautious that if the same instance is used for multiple calls, these variables might retain their state. Since LeetCode instantiates the solution class once per test case, it should be fine, but in general, it's better to avoid instance variables for such state if possible. You could pass state through parameters or use a non-recursive approach to avoid recursion stack limits for very deep trees, but that is beyond the scope of this problem.

Overall, your solution is excellent. With a minor optimization to stop early, it would be even more efficient.