Conversion Rate - Track and Query Funnel Step Conversion Rates

Question

## Problem

A product funnel has ordered steps: `["landing", "signup", "onboarding", "purchase"]`. Each user event is `(user_id, step, timestamp)`.

A "conversion" from step A to step B means a user completed step A and then later completed step B (not necessarily immediately after).

Implement:

```python
def conversion_rates(
    events: list[tuple[str, str, int]],
    funnel: list[str]
) -> list[float]:
    # returns conversion rate for each consecutive step pair
    # e.g. [signup/landing, onboarding/signup, purchase/onboarding]
```

## Example

```
events show 100 users reached "landing",
80 later reached "signup", 50 reached "onboarding", 20 reached "purchase"
Output: [0.80, 0.625, 0.40]
```

## Follow-ups

1. A user may complete the same step multiple times -- do you count the first occurrence only?
2. How would you add a time-window constraint (conversion only counts if it happens within 7 days of the prior step)?
3. Write this as a SQL query given a table `events(user_id, step, event_time)`.
4. How would you visualize drop-off and identify which step loses the most users?

Conversion Rate - Track and Query Funnel Step Conversion Rates

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