Factory Cost: Model a Manufacturing Factory with OOP and Compute Production Costs

Question

## Problem

Design an OOP model for a manufacturing factory. A `Factory` has multiple `ProductionLine`s. Each `ProductionLine` has a list of `Machine`s. Each `Machine` has an hourly operating cost and an output rate (units/hour).

Implement:
- `Factory.total_cost(hours)` — total operating cost across all machines for `hours` hours.
- `Factory.total_output(hours)` — total units produced.
- `Factory.cost_per_unit(hours)` — total cost / total output (raise `ValueError` if output is 0).

```python
class Machine:
    def __init__(self, hourly_cost: float, output_rate: float): ...

class ProductionLine:
    def __init__(self, machines: list): ...

class Factory:
    def __init__(self, lines: list): ...
    def total_cost(self, hours: float) -> float: ...
    def total_output(self, hours: float) -> float: ...
    def cost_per_unit(self, hours: float) -> float: ...
```

**Example:**
```
m1 = Machine(hourly_cost=50, output_rate=100)
m2 = Machine(hourly_cost=30, output_rate=60)
line = ProductionLine([m1, m2])
factory = Factory([line])

factory.total_cost(8)    -> 640.0
factory.total_output(8)  -> 1280.0
factory.cost_per_unit(8) -> 0.5
```

## Follow-ups

1. How would you add machine downtime (a machine is idle for some fraction of hours)?
2. How would you model a machine that has a fixed startup cost in addition to hourly cost?
3. How would you make this serializable to JSON for persistence?
4. How would you design a `simulate` method that runs production hour by hour and logs output?

Factory Cost: Model a Manufacturing Factory with OOP and Compute Production Costs

Question Details

Full Details

Topics

More from Stripe