completed trees - 3

[yashhh-23]

No description provided.

[Copilot]

Pull request overview

Adds Java binary-tree path-sum solution code (DFS + backtracking) to the repository.

Changes:

• Added a pathSum (Path Sum II) implementation using recursion, path tracking, and backtracking.
• Added the same implementation in two separate files (symmetrictree.java and pathsum2.java).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
symmetrictree.java	Adds a DFS/backtracking pathSum solution (currently duplicated and file name does not match implementation).
pathsum2.java	Adds a DFS/backtracking pathSum solution (same implementation as symmetrictree.java).

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[super30admin]

Path Sum II (pathsum2.java)

Strengths:

• Excellent use of backtracking technique, which is the optimal approach for this problem
• Time complexity is better than the reference solution (O(n) vs O(n²))
• Clean, readable code with good comments explaining the approach
• Proper handling of edge cases (empty tree)
• Correctly creates new ArrayList when adding to result to avoid reference issues

Areas for Improvement:

• The comment about "local and global variables not being updated correctly" suggests initial confusion about pass-by-value vs pass-by-reference in Java - this is worth understanding deeply for future tree problems
• Could add null check for targetSum parameter for robustness (though not required by constraints)

Minor Note:
The solution is actually more efficient than the reference solution in terms of time complexity due to the backtracking approach avoiding path copying.

VERDICT: PASS

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Symmetric Tree (symmetrictree.java)

The code quality itself is good - the backtracking is implemented correctly, comments are clear, and the solution follows good practices for the Path Sum II problem. However, you've solved the wrong problem entirely.

Key issues:

1. Wrong problem: The code solves "Path Sum II" but the problem asks for "Symmetric Tree"
2. Wrong return type: Should return boolean, not List<List>
3. Wrong method name: Should be isSymmetric, not pathSum
4. The comments and approach are completely misaligned with the problem

To solve the Symmetric Tree problem correctly:

• Use a recursive or iterative approach comparing left and right subtrees
• For recursion: compare root.left with root.right, then recursively check if left.left matches right.right and left.right matches right.left
• For iterative: use a queue to compare nodes in pairs (similar to the reference solution)

VERDICT: NEEDS_IMPROVEMENT