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Two Sum · Medium
Two Sum Medium
Problem Discussion

Given an array of integers nums and an integer target, return indices of the two numbers that add up to target.

You may assume each input has exactly one solution, and you may not use the same element twice.

Example

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: nums[0] + nums[1] = 9

Constraints

2 ≤ nums.length ≤ 104

solution.pytests
1def twoSum(nums, target): 2 seen = {} 3 for i, n in enumerate(nums): 4 diff = target - n 5 if diff in seen: 6 return [seen[diff], i] 7 seen[n] = i
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OA-style problems where each level adds complexity. Start with the basics, unlock harder levels as you go — just like the real online assessments.

In-Memory Database · Hard
2 Transactions
Level 2 / 4
Add transaction support
Implement BEGIN, COMMIT, and ROLLBACK operations
Level 1 · Basic GET/SET/DELETEDone
2Level 2 · TransactionsCurrent
3Level 3 · Nested transactionsLocked
4Level 4 · Expiry & persistenceLocked
solution.pytest_db.pyREADME.md
class Database: def begin(self): # Start a new transaction pass def commit(self): pass def rollback(self): pass
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Word Guessing Game · Medium
Files
PYgame.py
PYtests.pyread-only
Part 1 Debug
game.py
1class WordGame: 2 def __init__(self, word): 3 self.secret_word = word.lower() 4 self.guessed = set() 5 self.wrong = 0 6 7 def guess(self, letter): 8 letter = letter.lower() 9 self.guessed.add(letter) 10 if letter in self.secret_word: 11 return "correct" 12 self.wrong += 1 13 return "wrong"
Console Test Results AI Submissions
U
3 tests are failing. The losing condition seems off — can you check?
Thinking...
Looking at get_status(). The condition wrong_guesses > max_wrong uses > but should be >=. Also get_remaining_guesses has an off-by-one.

I see two bugs in game.py:

1. get_status() line 125 — should be >= not >:

if self.wrong_guesses >= self.max_wrong:
    return "lost"

2. get_remaining_guesses() has an off-by-one:

return self.max_wrong - self.wrong_guesses

Fix both and the tests should pass.

Why >= matters? Third bug?
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Design DoorDash
2 Architecture
How To Your Answer Feedback
Draw the architectureSketch the main components: mobile/web clients, API gateway, microservices, databases, and message queues.
Show data flowUse arrows to show how an order flows from the customer through the system. Label protocols (HTTP, gRPC).
Consider scalePeak dinner hours drive 10x traffic. Where do you add caching? What needs async processing?
Your work is on the canvas
Draw your architecture diagram on the right
No feedback yet
Click Check to get AI evaluation
HTTP gRPC events Mobile App iOS / Android Web App React API Gateway Load Balancer Order Service core logic Restaurant Svc menus & status Redis cache PostgreSQL primary DB Kafka event bus Notifications push / SMS Analytics dashboards
85Good

Strengths:

Clean microservice separation. Good use of event-driven architecture with Kafka for async workflows. Redis caching for menu/restaurant data is solid.

Areas to improve:

Consider a dedicated delivery matching service. Add a payment service between order and restaurant. WebSocket for real-time order tracking.

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Title
Rate Limiter
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Medium
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class RateLimiter: def __init__(self, limit): pass
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AlgorithmsData StructuresMulti-Level

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