Plaid Coding Interview Questions
100 Plaid coding interview problems with full optimal solutions — 31 easy, 50 medium, 19 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Plaid interviewer values, and a FAQ section.
Showing 4 problems of 100
- #58hardfrequently asked
58. Minimum Window Substring
Find the smallest window in a string containing all characters of a pattern. Plaid asks this because finding the smallest time window covering all required transaction-types in a feed (e.g., debit, credit, fee) is the same primitive.
- #83hardfrequently asked
83. Merge k Sorted Lists
Merge k sorted linked lists into one sorted list. Plaid asks this because merging k pre-sorted bank-feed streams into a unified ledger is exactly this primitive — it's their core ETL fan-in operation.
- #88hardfrequently asked
88. Trapping Rain Water
Compute how much water can be trapped between vertical bars. Plaid asks this as a two-pointer + running-max problem — the same shape they use to compute the cumulative un-allocated liquidity across a fluctuating balance series.
- #100hardfrequently asked
100. Serialize and Deserialize Binary Tree
Design serialize/deserialize for a binary tree. Plaid asks this because their merchant-category tree must be snapshot-able for caching and idempotent replay — they need a stable, deterministic serialization that survives round trips.