Five short string problems, all reported from Delivery Hero's live-coding and bar raiser rounds. None needs a framework; what the interviewer watches is how you pin down an underspecified problem, how you walk a string with indexes instead of reaching for a library call, and whether you can write the test cases yourself. Task 4 (Valid Word Abbreviation, from a 2026 bar raiser) is the same two-pointer skill as Task 3: parse a digit run as a count and move the pointers past it without expanding anything. Task 5 ends with a rewrite in streams and lambdas, because the interviewer wanted to see the candidate is comfortable with modern Java. Delivery Hero runs this on CoderPad with no autocomplete, so practise with the IDE's suggestions switched off. Time box: 45 minutes for all five; in the real round expect one or two of them.
- Java 21, JUnit 5, AssertJ 3, Maven wrapper. No Spring, no database.
- JDK 21+
./mvnw test. The first real test is@Disabled("story 1: remove this line to begin").
One user story at a time. Open INTERVIEW_TASKS.md, cover everything
below the current task, start a timer.
git checkout solutions/string-drills then ./mvnw test.
Reset to the skeleton: git checkout main -- java/string-drills.