Max Streak Length - Longest Consecutive Daily Activity Streak

Question

## Problem

Given a list of `(user_id, date_string)` activity records (dates in `"YYYY-MM-DD"` format), compute the longest streak of consecutive days each user was active. A streak is broken when there is a gap of more than one calendar day.

Return a dict `{user_id -> max_streak_length}`.

```python
def max_streaks(records: list[tuple[str, str]]) -> dict[str, int]:
```

## Example

```
records = [
  ("u1","2024-01-01"),("u1","2024-01-02"),("u1","2024-01-04"),
  ("u2","2024-01-01"),("u2","2024-01-02"),("u2","2024-01-03"),
]
Output: {"u1": 2, "u2": 3}
```

Note: duplicate dates for the same user count as one active day.

## Follow-ups

1. How would you write this as a SQL query over a `user_activity(user_id, activity_date)` table?
2. What if a "streak" allows one gap day (i.e., missing a single day does not break it)?
3. Return the date range `(start, end)` of the longest streak per user, not just the length.
4. The dataset has 50M rows. How do you process this efficiently in Python or Spark?

Max Streak Length - Longest Consecutive Daily Activity Streak

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