Completed Trees 1

[sanjoli97]

No description provided.

[super30admin]

Validate Binary Search Tree (ConstructBTFromPreAndInOrderTraversal.java)

• Major Issue: The submitted solution solves a completely different problem. Please ensure you're implementing the solution for the problem that was assigned.
• If working on BST validation: The reference solution demonstrates the correct approach using in-order traversal with a prev pointer to track the last visited node value.
• Key insight for BST validation: In a valid BST, an in-order traversal will produce a strictly increasing sequence. By tracking the previous node and comparing, we can validate the BST property.
• Code quality: The code you wrote is well-structured for its intended problem (tree construction), with good use of HashMap for O(1) lookups and clear documentation.

VERDICT: NEEDS_IMPROVEMENT

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Construct Binary Tree from Preorder and Inorder Traversal (ValidBST.java)

Strengths:

• The code is clean, well-documented, and follows good coding practices
• The BST validation logic is correctly implemented using inorder traversal
• Proper use of early termination when flag becomes false
• Good variable naming (flag, prev)

Critical Weakness:

• This is the wrong problem entirely. The submission validates whether a binary tree is a valid BST, but the problem asks to construct a binary tree from preorder and inorder traversals. The student appears to have submitted code for a different LeetCode problem.

Recommendation:
The student needs to implement the correct algorithm for constructing a binary tree from preorder and inorder traversals. The reference solution shows the correct approach:

• Use preorder's first element as the root
• Find this root's position in inorder to divide left and right subtrees
• Recursively build left and right subtrees
• Use a hashmap for O(1) lookup of inorder indices

VERDICT: NEEDS_IMPROVEMENT