Trees-2

[nagasai67]

No description provided.

[super30admin]

Construct Binary Tree from Inorder and Postorder Traversal (constructBinaryTree.py)

Strengths:

• The solution correctly implements the recursive algorithm with a hashmap for efficient index lookup.
• The time and space complexity are optimal.
• The code is clean and well-commented.

Areas for Improvement:

• While using self.post_idx is acceptable, it might be considered a bit unconventional because it uses an instance variable for a recursive state that is only relevant during the construction. This could be avoided by using a local variable and a nested function that modifies it (via closure) or by passing the index as a parameter (though that might require a wrapper or different structure). Alternatively, you could use an iterative approach without recursion to avoid stack overflow for very large trees, but recursion is generally acceptable for this problem given the constraints.
• The solution does not handle the case where the input arrays are empty. However, the constraints state that the length is at least 1, so it is not strictly necessary. But for robustness, you could add a check at the beginning for empty arrays.
• The helper function is defined inside the main function, which is fine, but note that in Python, defining a function inside another function might lead to a slight overhead due to closure. However, this is negligible for this problem.

Overall, the solution is excellent.

VERDICT: PASS

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Root to Leaf Sum (sumRootToLeaf.py)

Your solution is well-implemented and follows a similar approach to the reference solution. Here are some strengths and minor suggestions:

Strengths:

• You correctly use DFS recursion to traverse the tree, which is efficient and straightforward for this problem.
• The code is clean and well-commented, making it easy to understand.
• You correctly handle the base case (node is None) and update the current number appropriately.
• You correctly check for leaf nodes and update the result.

Areas for Improvement:

• While using a class variable self.res is acceptable, it might be slightly more efficient to avoid instance variables and instead return values from the helper function. However, this is a minor point and your approach is valid.
• Consider adding type hints for the helper function parameters to enhance readability and maintainability. For example, you could specify r: Optional[TreeNode] and num: int.
• The helper function does not return any value (it modifies self.res), which is fine, but an alternative approach could use a recursive function that returns the sum for the subtree, avoiding the need for a class variable. This would be more functional and avoid side effects. For example:

  def helper(r, num):
      if r is None:
          return 0
      num = num * 10 + r.val
      if r.left is None and r.right is None:
          return num
      return helper(r.left, num) + helper(r.right, num)

  Then you can call return helper(root, 0) without needing self.res. This approach is equally efficient and might be considered cleaner.

Overall, your solution is excellent. The suggestions are optional and meant to provide alternative perspectives.

VERDICT: PASS