PBT / Example Testing comparison problem

requirements.md

You are writing simple budgeting softare. A Budget consists of a total limit, represented as a positive integer, and a dictionary of category limits, represented as a map from strings to integers. For example:

{
  "total_limit": 50,
  "category_limits": {
    "food": 10,
    "rent": 11,
    "candles": 49
  }
}

(You can assume that no category will have a higher limit than the total, but you don't have to enforce this.)

A Bill is an array of Items. Each Item has a cost (positive integer), an optional count (positive integer), and optional categories (array of strings). For example:

[
  {"cost": 5},
  {"cost": 1, "count": 3},
  {"cost": 2, "categories": ["food", "gym"]},
  {"cost": 1, "count": 2, "categories": ["transit"]}
]

The goal is to write can_afford(budget, bill). Affordability is calculated under the following rules:

• The cost of every item is subtracted from total_limit.
• If an item shares a category with the budget's category_limits, then price of that item is also subtracted from said category in addition to the total_limit.
• The item might not share a category with the budget, or it might not have a category field at all. In both cases, no special rules apply.
• If an item shares multiple categories with the budget, the cost is applied to only one category limit of your choice.
• If an item has a count, the cost of the item is included count times. This applies to both total_limit and the category limits. If the count field is missing, you can assume a count of 1.
• can_afford is true if, after all items are accounted for, total_limit and all category limits are non-negative. If the total_limit or any category limits are below 0, then can_afford is false.

can_afford should be as permissive as possible. The following is considered affordable:

can_afford(
  {"total": 5, "category_limits": {"a": 1, "b": 3}},
  [{"cost": 2, "categories": ["a", "b"]}]
)

While the sole item in the bill is greater than category_limits[a], it is less than category_limits[b], so the bill is affordable.

You do not need to use the same names for anything, or the same data layout, as long as the requirements are satisfied.

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ROT13 spoilers:

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they are encrypted with ROT8

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Reading and code breaking are not my strongest suits