The conditions look straightforward but i kept second-guessing which rule took priority.
Clarify the exact age-based eligibility rules (e.g., no requests if age < 13, no requests between users with age difference > 2, etc.) and then design an efficient algorithm, likely using sorting and two pointers or binary search, to count valid pairs without enumerating all O(n^2) pairs. Discuss time and space complexity and handle edge cases like empty list or all same ages.
Pro tip: Mention that you would first confirm the rules with the interviewer, as they are not fully specified, and then propose a solution that scales to large inputs, showing you think about production constraints at Meta.
Ask the interviewer to specify the exact age-based eligibility conditions, such as minimum age, maximum age difference, and any other constraints (e.g., same age allowed).
Recognize this as a counting problem over pairs with constraints, which can often be solved efficiently by sorting and using two pointers or binary search.
Sort the ages, then for each user, find the range of other users whose ages satisfy the conditions, and count valid pairs using two pointers or binary search, avoiding double counting.
State the time complexity (e.g., O(n log n) due to sorting) and space complexity (O(1) extra if sorting in place), and discuss trade-offs.
Walk through a small example to verify correctness, including edge cases like empty list, single user, or all ages identical.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.