PreCourse 1 complete

[vishalmgvk]

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[super30admin]

Exercise 1: myStack Class

Strengths:

• Clean, simple implementation using Python's list
• All basic stack operations (push, pop, peek, isEmpty, size) are correctly implemented
• Good use of Python's built-in methods for O(1) operations

Issues:

• Critical Bug: No bounds checking - pop() on an empty stack raises IndexError. Should return None or raise a custom exception.
• Encapsulation Issue: show() returns the internal list directly, allowing external code to modify the stack's internal state.
• Missing Documentation: No time/space complexity comments as requested in the problem description.

Exercise 2: Stack with Linked List

Strengths:

• Correct use of linked list for stack implementation
• Good O(1) push and pop operations
• Interactive menu is well-structured

Critical Issues:

• Design Flaw: Using Node(None) as a sentinel/dummy node is problematic. The check self.stack.data is None cannot distinguish between an empty stack and a stack with a legitimately pushed None value.
• Bug: If None is pushed as a value, pop() will incorrectly return None and treat it as an empty stack.
• Inconsistent Design: The dummy node approach is half-implemented and causes confusion.

Exercise 3: SinglyLinkedList

Strengths:

• Correct implementation of append, find, and remove operations
• Good handling of head node removal
• Proper traversal logic

Issues:

• Dead Code: self.node = ListNode() in __init__ creates a dummy node that is never used.
• No Feedback: remove() silently does nothing if key is not found - should return boolean or raise exception.
• Missing Methods: No __len__, __str__, or __repr__ for usability.
• Inefficiency: No size tracking - len() would require O(n) traversal.

General Recommendations

1. Add proper error handling for edge cases (empty stack, element not found)
2. Remove unused code (dummy node in Exercise 3)
3. Add docstrings with time/space complexity as requested
4. Consider returning boolean values from remove() operations
5. Use consistent sentinel node patterns if implementing them