Design-1 problems solution

[Simranb10]

Submit Design-1 problem solutions

[super30admin]

Implement Hash Set (MyHashMap.java)

Strengths:

• Good use of a separate Node inner class for encapsulation
• Reasonable variable naming and structure
• Attempted to handle collisions through chaining

Areas for Improvement:

• Critical: You implemented a HashMap instead of a HashSet. The problem requires storing only keys (no values), with methods add(), contains(), and remove(). Your implementation has put() and get() which are HashMap methods.
• The linked list approach is more complex than necessary. A simple boolean array approach (like the reference solution) would be more efficient and easier to implement.
• The getPrevious() method has convoluted logic that makes the code harder to follow.
• Consider using a boolean array instead of linked lists for O(1) guaranteed operations.

VERDICT: NEEDS_IMPROVEMENT

---

Implement Min Stack (MinStack.java)

Strengths:

• Good attempt at optimizing space by only tracking when minimum changes
• Clean variable naming and reasonable structure
• Correctly identifies O(1) time complexity

Areas for Improvement:

1. Critical Bug: The top() method returns incorrect values. When you push the previous minimum before the new value, the stack structure becomes corrupted for top operations.
2. Logic Flaw: The push logic if(min >= val) causes duplicate minimums to be pushed, which breaks the correspondence between the main stack and minimum tracking.
3. Consider using a two-stack approach: The reference solution uses a separate minSt stack that mirrors every push/pop operation, making the code more predictable and easier to debug.
4. Alternative fix: If keeping single stack, you need to ensure that top() always returns the actual top element, not a minimum value.

The core issue is that mixing data elements with minimum tracking elements in a single stack creates ambiguity about what top() should return.

VERDICT: NEEDS_IMPROVEMENT