Engineering Deep Dives

Learn how to solve Random Pick with Weight using prefix sums and binary search — plus exactly what interviewers expect and the mistakes that tank candidates.

Learn how to solve the Longest Common Prefix problem the way interviewers expect — column-by-column thinking, clean code, and zero panic.

Learn how to design a blob storage system like S3 in interviews — covering partitioning, metadata separation, replication, and the 10 mistakes that cost candidates the offer.

Master the 3Sum problem with Sort + Two Pointers, avoid the duplicate-skipping traps that trip up most candidates, and learn the pattern that unlocks a whole class of interview questions.

Learn how to solve the rotated sorted array problem in O(log n) — including what interviewers really look for, common mistakes that cost candidates the offer, and exactly how to talk through it.

Learn how to crack the Next Permutation problem in interviews — from building the right intuition to avoiding the exact mistakes most candidates make under pressure.

Most candidates overthink this problem and fall into classic binary search traps. Here's the clean lower_bound/upper_bound approach that interviewers love.