Completed Design-2 - #2493

Implement Queue using Stacks (Queue.java)

Strengths:

1. Your solution correctly implements the queue using two stacks with optimal amortized O(1) time complexity
2. Good use of comments to document your approach and time/space complexity
3. Defensive programming with the empty check in pop and peek is a nice touch
4. Clear variable naming makes the code easy to understand

Areas for Improvement:

1. Code Duplication: The transfer logic from inStack to outStack is duplicated in both pop and peek. Consider extracting this into a private helper method like private void transfer() to reduce duplication and improve maintainability.
2. Java Best Practice: In Java, Stack is a legacy class. Consider using Deque<Integer> with ArrayDeque implementation instead, which is more efficient and recommended for stack-like behavior. For example: Deque<Integer> inStack = new ArrayDeque<>();
3. Method Reuse: You could call peek() from pop() to avoid duplicating the transfer logic, similar to the reference solution.

Example Refactoring:

private void transfer() {
    while (!inStack.isEmpty()) {
        outStack.push(inStack.pop());
    }
}

public int pop() {
    if (empty()) return -1;
    if (outStack.isEmpty()) transfer();
    return outStack.pop();
}

public int peek() {
    if (empty()) return -1;
    if (outStack.isEmpty()) transfer();
    return outStack.peek();
}

VERDICT: PASS

Design HashMap (HashMap.java)

EESSENTIAL DETAILS: The student used 10000 buckets instead of 1000, but this is a minor difference and doesn't affect correctness. The logic is essentially identical to the reference solution. The student correctly implemented all four operations (put, get, remove) using a hash table with separate chaining (linked lists). The code is well-structured and readable. The student's solution is correct and efficient.

ESSENTIAL DETAILS: The student used 10000 buckets instead of 1000, but this is a minor difference and doesn't affect correctness. The logic is essentially identical to the reference solution. The student correctly implemented all all four operations (put, get, remove) using a hash table with separate chaining (linked lists). The code is well-structured and readable. The student's solution is correct and efficient.

VERDICT: NEEDS_IMPROVEMENT