Adding all the solutions

[subbu4061]

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[super30admin]

Let's evaluate each file separately:

Exercise_1.java (Array-based Stack Implementation):

• Correctness: The implementation correctly handles stack operations (push, pop, peek) with proper overflow/underflow checks. The isEmpty() method has a minor issue - it should check top == -1 (or similar) for an empty stack since top = 0 means there's one element.
• Time Complexity: Correctly identified as O(1) for all operations.
• Space Complexity: Correctly identified as O(1) for operations, though the overall stack space is O(n).
• Code Quality: Well-structured and readable. The overflow check in push() should be top >= MAX instead of top <= MAX.
• Efficiency: Good, but could add a constructor that initializes top to -1 for better empty stack representation.

Exercise_2.java (Linked List-based Stack Implementation):

• Correctness: Correctly implements stack operations with proper underflow checks. The isEmpty() method works correctly.
• Time Complexity: Correctly identified as O(1) for all operations.
• Space Complexity: Correctly identified as O(1) for operations.
• Code Quality: Excellent structure and readability. Good use of linked list nodes.
• Efficiency: Very efficient implementation with no obvious improvements needed.

Exercise_3.java (Singly Linked List Implementation):

• Correctness: Correctly implements insertion and printing of a linked list.
• Time Complexity: Correctly identified as O(n) for both insertion (due to traversal) and printing.
• Space Complexity: Correctly identified as O(1) for operations (though overall space is O(n)).
• Code Quality: Well-structured and readable. The insert method could be made more efficient by maintaining a tail pointer.
• Efficiency: While correct, maintaining a tail pointer would make insertions O(1) instead of O(n).

General Strengths:

1. Good documentation of time and space complexity
2. Proper error handling for stack operations
3. Clean, readable code structure
4. Appropriate use of data structures

Areas for Improvement:

1. Exercise_1's isEmpty() logic needs correction
2. Exercise_1's push() overflow condition should be >=
3. Exercise_3 could be optimized with a tail pointer
4. Consider adding more edge case tests (e.g., multiple pops on empty stack)