Add PreCourse-1 PR submission

[agk-s30]

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[super30admin]

Exercise_1.py

• Strengths: Clean implementation using Python list, correct handling of edge cases (empty stack returns None), all operations are O(1) as stated.
• Areas for Improvement: The comment "Please read sample.java file before starting" is unnecessary for a Python solution. Consider adding docstrings to methods for better documentation.

Exercise_2.py

• Strengths: Proper linked list-based stack implementation with O(1) push/pop operations. Good error handling when popping from empty stack.
• Areas for Improvement: The comment about EOF errors appears twice unnecessarily. The pop() method returns None but the main code doesn't handle the case where int(do[1]) might fail if input is malformed. Consider adding a peek() method for completeness.

Exercise_3.py

• Strengths: Well-documented linked list with clear docstrings explaining time complexities. Correctly handles edge cases (empty list, head removal, element not found).
• Areas for Improvement: The remove() method could benefit from returning a boolean to indicate success/failure. Consider adding a size() method for utility. The find() method returns the node, but typically users might want just the data.

General Observations:

• All three exercises correctly implement their respective data structures
• Time/space complexities are accurately stated
• Code is readable and well-structured
• Edge case handling is appropriate throughout