Coding questions

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1. Coding questions · PayPal

   Compare write-back vs write-through caches

   This question evaluates understanding of caching policies and memory/storage hierarchy trade-offs, focusing on how write-back and write-through handle writes, coherence, durability, latency, bandwidth, dirty bits, write amplification, and power-loss risks.

2. Coding questions · Confluent

   Complete a 9x9 Sudoku Puzzle That Has Exactly One Solution

   A coding problem that asks you to complete a 9x9 Sudoku puzzle that has exactly one solution, keeping every given digit and filling each row, column and 3x3 box with the digits 1 to 9. It tests constraint tracking and systematic search over the empty cells.

3. Coding questions · New Relic

   Compress a String by Run-Length Counts, Keeping the Original When Not Shorter

   Implement run-length string compression that replaces each run of repeated characters with the character and its count, returning the original string when the compressed form is not strictly shorter. Tests careful run handling, multi-digit counts, the tie rule, and complexity and edge-case discussion.

4. Coding questions · Amazon

   Compute 3-Day Rolling Revenue Averages with Pandas

   This question evaluates proficiency with Python pandas for time-series data manipulation, specifically group-wise aggregation, rolling-window calculations, pivoting, and merging summary statistics.

5. Coding questions · TikTok

   Compute 7-Day Rolling Average of Unique Post Viewers

   This question evaluates proficiency with SQL data manipulation, window functions for rolling aggregates, deduplication of user events, and text-filtering of metadata.

6. Coding questions · TikTok

   Compute 7-day rolling complaint/order ratio in SQL

   This question evaluates SQL data manipulation skills, specifically time-based aggregations, sliding window functions, joins to include entities with no events, and numeric casting within the Data Manipulation (SQL/Python) domain.

7. Coding questions · Meta

   Compute 7-day views and reactions by relationship

   This question evaluates skills in SQL-based data manipulation—specifically deduplication by longest duration, join-based attribution of reactions to views, window functions, distinct counts, aggregations, and date-range filtering within the Data Manipulation (SQL/Python) domain.

8. Coding questions · Meta

   Compute 95th-percentile call concurrency

   This question evaluates a candidate's ability to design scalable algorithms for computing the 95th-percentile of per-minute concurrent calls over a 24-hour window, testing competencies in streaming/event aggregation, de-duplication, percentile computation, and managing time and memory constraints.

9. Coding questions · Fetch Rewards

   Compute a Seven-Day Rolling Average

   This question evaluates proficiency with time-series aggregation and windowing concepts, specifically computing calendar-based 7-day rolling averages for a daily metric and using SQL window functions while handling missing dates.

10. Coding questions · Whatnot

    Compute a Seven-Day Rolling Average

    A PostgreSQL interview problem about computing a seven-day rolling average from dated observations. Candidates must use window frames carefully, preserve the requested grain, handle incomplete history, and return deterministically ordered results.

11. Coding questions · Meta

    Compute active ad revenue by creation source

    This question evaluates proficiency in data manipulation and analytics, testing skills such as joining event and impression tables, aggregating time-series revenue, and counting distinct active ads broken down by creation source.

12. Coding questions · Meta

    Compute ad impression conversion rates

    This question evaluates proficiency in time-based event attribution, aggregation of business metrics (impressions, conversion rates, spend and revenue), timestamp handling, and user/ad-level matching within the Data Manipulation (SQL/Python) domain, emphasizing practical application over abstract theory.

13. Coding questions · Coinbase

    Compute adoption, latency, and cross-region transactions

    This question evaluates proficiency in SQL-based data manipulation and analytics, including calculating cohort adoption and transaction rates, performing date arithmetic for time-to-first-transaction, identifying cross-region transactions, and computing distributional percentiles.

14. Coding questions · Meta

    Compute ads revenue by geography in SQL

    This question evaluates SQL data manipulation and revenue attribution skills, testing the ability to aggregate and compute business metrics such as total revenue, impressions, clicks, CTR, and revenue per 1k impressions from ad impressions, clicks, and billing records.

15. Coding questions · CVS Health

    Compute age-band spend and YoY in Georgia

    This question evaluates SQL data-manipulation competency including aggregations, percent-share calculations, year-over-year comparisons, join strategies, and handling NULLs and zero-value groups.

16. Coding questions · Yelp

    Compute and Rank by Jaccard Similarity

    The prompt evaluates set-based similarity metrics (Jaccard), robust tokenization and normalization for text data including Unicode and punctuation edge cases, streaming/iterator processing for very long inputs, and algorithmic efficiency for top-k retrieval and stable ranking.

17. Coding questions · TikTok

    Compute and rank top bad advertisers

    This question evaluates proficiency in SQL data manipulation and analytics, including time-window filtering, JOINs, aggregation and deduplication, rate calculations, and window-function–based ranking.

18. Coding questions · Roblox

    Compute ARPDAU/ARPPU by country

    This question evaluates data manipulation and analytics skills for computing user- and revenue-based metrics (ARPDAU, ARPPU), focusing on aggregation, multi-key joins, deduplication, time-window filtering, and correct revenue attribution.

19. Coding questions · Amazon

    Compute array modes with ties and no-mode rule

    This question evaluates algorithm design and data-structure skills—frequency counting, hashing, and handling edge cases such as ties and a no-mode rule—within the coding and algorithms domain for data scientist roles.

20. Coding questions · LinkedIn

    Compute article-type diversity per user and histogram

    This question evaluates data manipulation and aggregation skills, including joining event logs with metadata, deduplicating by categorical attribute, date-based filtering, and computing per-user distinct counts.

21. Coding questions · Instacart

    Compute average customer waiting time

    Compute average customer waiting time evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

22. Coding questions · TikTok

    Compute Averages of Unique Numbers in Dictionary Lists

    This question evaluates data manipulation and aggregation skills, focusing on handling duplicate values within collections and computing numerical summaries of list data.

23. Coding questions · Current

    Compute balances and array queries

    This question evaluates proficiency in data structures and algorithms, focusing on array processing, aggregation for computing per-user balances, and handling mutable range-sum queries.

24. Coding questions · Meta

    Compute binary tree left-side view

    This question evaluates understanding of binary tree traversal and level-order reasoning, including distinctions between recursive and iterative approaches and handling of edge cases such as skewed or missing children.