Arrays, Strings & Sliding Window

Arrays, strings, hashing, two-pointer and sliding window are the bread-and-butter band at Airbnb, around a fifth of the coding surface and the heart of the phone screen. They share a single move. You keep a window or a pair of pointers over the data, slide it forward, and maintain just enough running state to answer the question without re-scanning what you already passed.

The problems are standard. The grading is not. Your code has to compile and run against test cases in CoderPad while the interviewer watches, and pseudocode is not accepted. A window carries two or three indices that all have to move in lockstep. The bug that ships is almost always an off-by-one on a window edge, or a count that drifts out of sync. Airbnb wants to watch you hit that bug live, read your own failing output, and fix it without losing the thread.