Completed precourse1

[ashritha0806]

No description provided.

[super30admin]

Let's evaluate each file separately:

File: Exercise_1.py (Stack using list)

• Correctness: The implementation correctly uses a list to represent a stack. The push, pop, peek, isEmpty, size, and show methods are implemented correctly. However, the pop method returns a string when the stack is empty, which might be inconsistent with the expected data type (it should probably raise an exception). Similarly, peek doesn't return anything when the stack is empty (should return None or raise an exception).
• Time Complexity: The time complexities are correctly stated: O(1) for push, pop, peek, isEmpty, and size. However, note that in Python, list.append() is amortized O(1), and list.pop() from the end is O(1).
• Space Complexity: O(n) is correct for storing n elements.
• Code Quality: The code is clean and readable. However, the show method returns the internal list, which might break encapsulation (allowing external modifications). It might be better to return a copy or a string representation.
• Efficiency: The implementation is efficient for a stack using a list.

File: Exercise_2.py (Stack using linked list)

• Correctness: The Stack class is implemented using a linked list with a root pointer. The push and pop operations are correctly implemented. The pop method returns None when the stack is empty, which is handled appropriately in the test code. The test code provides an interactive session for pushing, popping, and quitting.
• Time Complexity: O(1) for push and pop, which is correct for a linked list stack.
• Space Complexity: O(n) for storing n nodes, which is correct.
• Code Quality: The code is well-structured. The Node class is defined appropriately. The interactive part is clear. However, the input handling assumes that the input is given correctly (e.g., for push, there must be a second value). If the user inputs "push" without a value, it will crash with an IndexError. This could be improved with error handling.
• Efficiency: The implementation is efficient.

File: Exercise_3.py (Singly linked list)

• Correctness: The SinglyLinkedList class has append, find, and remove methods. Append adds to the end (O(n)), find searches for a key (O(n)), and remove removes the first occurrence (O(n)). The remove method returns True if found and removed, False otherwise. This is correct. However, note that the remove method does not actually free the node (but in Python, garbage collection handles this). Also, the remove method updates the head correctly when removing the first node.
• Time Complexity: The time complexities are correctly stated: O(n) for append, find, and remove. However, append could be optimized to O(1) by maintaining a tail pointer.
• Space Complexity: O(1) for the operations is not entirely accurate. The space complexity of the data structure is O(n) for storing n elements. The operations themselves use constant extra space (O(1)), which is probably what was meant.
• Code Quality: The code is clear. The ListNode class is defined appropriately. The methods are well-named. However, the append method could be optimized by storing a tail pointer to avoid traversing every time.

Overall:
Strengths:

• The student has implemented the data structures correctly for the most part.
• Time and space complexities are generally correctly stated.
• Code is readable and well-structured.

Areas for improvement:

• In Exercise_1.py, consider handling empty stack cases with exceptions or consistent return types.
• In Exercise_2.py, add error handling for invalid inputs (e.g., push without a value).
• In Exercise_3.py, consider adding a tail pointer to make append O(1). Also, clarify space complexity: the data structure uses O(n) space, but each operation uses O(1) extra space.