Funnel Conversion Count

Problem Given each user's chronological event stream and an ordered funnel of steps (e.g. signup → add_to_cart → purchase), count how many users completed each step, where the steps must occur in the given order.

Input / Output

• Input: per-user lists of timestamped events, and the ordered funnel steps.
• Output: for each funnel step, the number of users who reached it (having done all prior steps in order).

Constraints

• Steps must occur in the funnel order (a later step counts only if the earlier ones happened before it).
• Streams may contain unrelated events and repeats.

Example

• Funnel [signup, add_to_cart, purchase]; a user with signup, add_to_cart, logout counts toward steps 1 and 2 but not 3.