Complete Trees-3

[satish-paraddi]

No description provided.

[super30admin]

Path Sum II (Problem1.py)

Strengths:

1. Excellent use of backtracking with path.pop() — this is more memory-efficient than the reference solution's pass-by-value approach
2. Clean, readable code with good variable naming
3. The remaining variable approach is intuitive and easy to follow
4. Proper handling of leaf nodes and the target sum check
5. Using list(path) when appending to results correctly creates a copy to avoid reference issues

Areas for Improvement:

1. Space complexity comment is slightly misleading: The comment says O(n) auxiliary space, but the recursion stack itself can be O(n) deep, and the output storage is O(n²) in the worst case. Consider clarifying this in the comment.
2. Edge case handling: While the code handles None nodes correctly, you could add an early return for root is None at the start of pathSum for clarity (though it's not strictly necessary since dfs handles it).
3. Optional optimization: You could avoid the list(path) copy by using path[:] or restructuring, but list(path) is perfectly fine and Pythonic.

Overall, this is a high-quality solution that demonstrates a solid understanding of DFS with backtracking. The approach is actually slightly more elegant than the reference solution due to the in-place backtracking.

VERDICT: PASS

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Symmetric Tree (Problem2.py)

Strengths:

1. Correctness: The solution correctly handles all edge cases, including when both nodes are null, when one is null, and when values differ.
2. Recursive approach: The recursive solution is clean and easy to understand, leveraging the natural structure of the problem.
3. Space complexity: The recursive approach has O(h) space complexity, which is better than the iterative approach's O(n) in balanced trees.
4. Code quality: The code is well-structured, readable, and follows best practices. The student has also provided comments on the time and space complexity.

Areas for improvement:

1. Iterative approach: The problem statement mentions a follow-up to solve it both recursively and iteratively. The student could consider implementing an iterative solution using a queue or stack to demonstrate versatility.
2. Edge case handling: While the solution handles edge cases correctly, the student could add more explicit comments or documentation to explain the logic.

VERDICT: PASS