Consecutive Login Failures | Dataford Interview Questions

Jane Street's login audit stream contains chronological events for each user. Given these events and an integer k, flag every user who has at least one consecutive run of exactly k failed logins.

A failure run counts only when it is bounded by a successful login or the beginning or end of that user's event list. A run of more than k failures does not qualify, because its full consecutive run is not exactly k.

Formal Specification

Implement flag_users(user_events, k), where user_events is a dictionary mapping a user ID string to a list of event strings, each either `

Constraints

1 <= len(user_events) <= 10^5
0 <= len(user_events[user]) <= 10^5
The total number of events across all users is at most 10^6
k >= 1
Every event is either "Success" or "Fail"
User IDs are unique strings

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Problem

Jane Street's login audit stream contains chronological events for each user. Given these events and an integer k, flag every user who has at least one consecutive run of exactly k failed logins.

Formal Specification

Implement flag_users(user_events, k), where user_events is a dictionary mapping a user ID string to a list of event strings, each either `

Constraints

1 <= len(user_events) <= 10^5
0 <= len(user_events[user]) <= 10^5
The total number of events across all users is at most 10^6
k >= 1
Every event is either "Success" or "Fail"
User IDs are unique strings

Your question is Consecutive Login Failures. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.