adding arrays-1 solutions

[nikhylw]

solution 1 - product except self - W3_product_except_self.py
solution 2 - matrix diagonal traversal - W3_diagonal_traverse.py

[super30admin]

Product Except Self (W3_product_except_self.py)

Strengths:

• Excellent implementation of the two-pass prefix/suffix product technique
• Correctly achieves O(n) time complexity, which is optimal for this problem
• Uses O(1) extra space, meeting the follow-up requirement
• Clean, readable code with good comments
• Proper handling of edge cases (works for any valid input length ≥ 2)

Areas for Improvement:

• The if nums is None check is unnecessary since the problem guarantees nums will be a valid list (and checking for None with a list in Python is typically if nums is None not if nums is None). This check could be removed for cleaner code.
• Consider adding a brief docstring to the method explaining its purpose and approach.

Minor Note:
The reference solution provided is actually a naive O(n²) solution, while the student's solution correctly implements the optimal O(n) approach. The student should be aware that their solution is superior to the reference provided.

VERDICT: PASS

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Diagonal Traverse (W3_diagonal_traverse.py)

Strengths:

• Clean and readable code structure
• Correct algorithm implementation with proper boundary handling
• Good variable naming conventions
• Efficient O(m*n) time complexity
• Proper use of comments explaining complexity

Areas for Improvement:

• Add a check for empty matrix input: if not mat or len(mat) == 0: return [] to prevent IndexError when mat is empty
• Consider adding docstring to document the function's purpose and parameters
• The initial check if mat is None is somewhat redundant in Python (empty list check would be more useful)

VERDICT: PASS

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Spiral Matrix

Strengths:

• The code is clean, well-documented, and follows good coding practices
• Both solutions achieve optimal time and space complexity
• Edge cases are handled appropriately
• The diagonal traverse solution correctly handles boundary conditions

Areas for Improvement:

• Critical Issue: The student submitted solutions for the wrong problem. The assignment was to solve "Spiral Matrix" but the files contain "Diagonal Traverse" and "Product Except Self" solutions.
• The student should ensure they are solving the exact problem specified in the assignment
• For the diagonal traverse solution, the initial if mat is None check could be improved to if not mat to also catch empty lists

VERDICT: NEEDS_IMPROVEMENT