Added implementation

[Balaviknesh]

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[super30admin]

Let's evaluate each exercise one by one.

Exercise_1.kt (Array-based Stack):

• Correctness: The implementation correctly handles stack operations (push, pop, peek, isEmpty) with proper overflow and underflow checks. The driver code demonstrates basic functionality.
• Time Complexity: As stated, all operations are O(1), which is optimal for a stack.
• Space Complexity: O(MAX) is correct, but note that MAX is fixed at 1000, so it's O(1) in terms of variable input size. However, since the problem states MAX=1000, it's acceptable.
• Code Quality: The code is clean and readable. However, returning 0 in pop() and peek() under error conditions might be problematic if 0 is a valid value. Consider throwing an exception or using nullable types (Int?) to better handle errors.
• Efficiency: The implementation is efficient for the given constraints.

Exercise_2.kt (Linked List-based Stack):

• Correctness: The implementation is correct for a linked list-based stack. It handles underflow conditions by printing a message and returning 0.
• Time Complexity: All operations are O(1), as expected.
• Space Complexity: O(n) is correct, where n is the number of elements.
• Code Quality: The code is well-structured. However, similar to Exercise_1, returning 0 for underflow might be error-prone. Using exceptions or nullable types would be better. Also, the use of !! (not-null assertion) is safe here because isEmpty() is checked first, but it's generally better to avoid !! when possible. Using safe calls or conditional checks would be more idiomatic.
• Efficiency: The implementation is efficient.

Exercise_3.kt (Linked List Insertion):

• Correctness: The insert function correctly appends nodes to the end of the list. However, the function returns the same list it was given (with head potentially updated), which might be confusing. Since the head is updated in-place, returning the list is redundant. Also, the function does not handle the case where the list is empty efficiently (it already does with the null check).
• Time Complexity: Insertion is O(n) per operation because it traverses to the end each time. This is standard for appending without a tail pointer.
• Space Complexity: O(n) is correct.
• Code Quality: The code is readable, but the insert function could be improved by maintaining a tail pointer to avoid O(n) per insertion. Alternatively, consider inserting at the head for O(1) insertion (but then the order would be reversed). Also, the function returns the list, but it modifies the list in-place. This might lead to confusion. It would be better to not return anything (Unit) or to clearly document the behavior.
• Efficiency: For frequent appends, maintaining a tail pointer would improve efficiency.

General Comments:

• The student has provided time and space complexity comments at the top of each file, which is good.
• The code follows the problem requirements and uses appropriate data structures.
• Error handling could be improved by using exceptions or nullable types instead of returning 0.
• The linked list in Exercise_3 could be optimized with a tail pointer for O(1) appends.

Overall, the solutions are correct and efficient for the given problems, with minor improvements possible in error handling and code structure.