Design a weighted random value generator

## Weighted random value generator Design a generic component that stores values with integer weights and can return a random value with probability proportional to its weight. ### Requirements - Support adding a value with a weight: - `add(value: T, weight: Int)` - Support returning a random value: - `pick(): T` (name can vary) - If the stored pairs are `[(1,1), (2,1), (5,3)]`, then probabilities are: - `1`: 20%, `2`: 20%, `5`: 60% - If you then add `(3,5)`, probabilities become: - `1`: 10%, `2`: 10%, `5`: 30%, `3`: 50% ### Focus Prioritize **clarity, maintainability, and extensibility** over micro-optimizing performance. ### Follow-up Add an API that supports expiration: - `addWithExpiry(value: T, weight: Int, expireAfterMs: Int)` - After the expiration time elapses, that added weight contribution should no longer affect `pick()`. ### Clarifications to address (state assumptions) - Whether `weight` is always positive. - Whether adding an existing `value` merges weight or stores multiple entries. - Expected behavior when there are no active (non-expired) entries.