15-112: Fundamentals of Programming and Computer Science
Week 4 Practice Problems

Try the problems listed here (some of which we reviewed in lecture and recitation).

Also, check out recent semesters' strings hw's (usually week3 or week4), and the quizzes those same weeks. You'll find great practice problems like encodeRightLeftRouteCipher and decodeRightLeftRouteCipher, and many others!