GPU Credit Calculator - Compute Cost and Remaining Credits for GPU Usage

Question

## Round 1 - Coding

## Problem

Design a GPU credit system used by an ML platform. Users have a credit balance and submit GPU jobs with an instance type and duration. Different instance types have different costs per hour. Implement the credit management system.

```python
GPU_COSTS = {
    "T4":  0.35,   # credits per hour
    "A100": 3.00,
    "H100": 8.00,
}

class GPUCreditSystem:
    def __init__(self, initial_credits: float): ...

def run_job(
        self,
        instance_type: str,
        duration_hours: float
    ) -> dict:
        # Returns {"success": bool, "cost": float, "remaining": float}
        # Deducts cost if sufficient credits; otherwise rejects the job
        ...

def add_credits(self, amount: float) -> float:
        # Returns new balance
        ...

def get_balance(self) -> float: ...
```

```
Example:
sys = GPUCreditSystem(initial_credits=10.0)
sys.run_job("T4", 2.0)   -> {"success": True,  "cost": 0.70, "remaining": 9.30}
sys.run_job("H100", 5.0) -> {"success": False, "cost": 40.0, "remaining": 9.30}
```

## Follow-ups

1. How would you track a usage history per user for auditing?
2. What concurrency issues arise if two jobs submit simultaneously with insufficient combined credits?
3. How would you implement a soft limit (warn at 20% remaining) vs. a hard limit?
4. How would you handle fractional hours (job runs 90 minutes)?

GPU Credit Calculator - Compute Cost and Remaining Credits for GPU Usage

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