Strings — DSA Interview Problems

Strings is arrays of characters with their own rich set of interview patterns, and it shows up very frequently in technical interviews. String questions probe two-pointer and sliding-window fluency, frequency counting, and careful index handling.

Our library indexes 55 Strings problems (29 easy, 21 medium, 5 hard), each solved brute-force → optimal in Java and Python with a line-by-line walkthrough and interview talking points. They're grouped below by the curriculum module that teaches the underlying pattern, so related problems reinforce one another.

If you remember one thing about Strings, make it this: A character-frequency array or map turns most 'substring' questions into a sliding-window scan. Once that clicks, the signature patterns — sliding window, two pointers, frequency maps, hashing — start to feel like a checklist you run on every new problem.