Completed PreCourse-1 exercises in Python

[allurkarsneha]

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[super30admin]

Exercise_1.py (Array-based Stack):

• Correctness: The implementation is correct with all core operations (isEmpty, push, pop, peek, size, show) working as expected.
• Time Complexity: The stated complexities are accurate. Push is O(1) amortized due to Python list's dynamic array behavior.
• Space Complexity: O(n) is correct.
• Code Quality: Good, clean implementation. Minor improvement: could use elif instead of separate if/else blocks for consistency.

Exercise_2.py (Linked List-based Stack):

• Correctness: The implementation is correct with proper head insertion for push and head removal for pop.
• Time Complexity: O(1) for both operations is correct.
• Space Complexity: O(n) is correct.
• Code Quality: Good structure. The interactive menu is well-implemented. Consider adding type hints for better readability.

Exercise_3.py (Singly Linked List):

• Correctness: The implementation is correct. All operations (append, find, remove) work properly, including edge cases like removing head, middle, and tail nodes.
• Time Complexity: All stated O(n) complexities are accurate.
• Space Complexity: O(n) for storage and O(1) for operations is correct.
• Code Quality: Well-documented with clear docstrings. Good variable naming. The test cases are comprehensive and demonstrate proper handling of edge cases.

General Observations:

• All three exercises demonstrate solid understanding of data structures (stack using array, stack using linked list, singly linked list).
• Time and Space complexity analysis is included as requested.
• Code is well-structured with clear separation of concerns.
• Edge cases are handled appropriately (e.g., pop/peek on empty stack, remove from empty list).