AP CSA FRQ Guide
2008 FRQ 2: StringCoder
Decode a list of string parts by joining substrings from a master string, then encode a word by repeatedly finding a part that matches its remaining prefix.
Substring Encoding with ArrayList22 minute targetStringArrayListsubstringobjectshelper methods
Skills Tested
What this FRQ is really practicing
StringArrayListsubstringobjectshelper methods
Review these topics before attempting the problem.
Starter Approach
How to begin with your own plan
- 1Part A: retrieve the substring at each StringPart start with its specified length and concatenate the substrings in list order.
- 2Part B: use findPart to match the beginning of the remaining word, append that StringPart to the result, and advance by its length.
- 3Continue encoding until the entire word is represented, preserving the part order.
Attempt the problem before opening the solution.
Common Mistakes
Mistakes to watch for while writing
Using the part length as an absolute substring end index.
Calling findPart on the original word on every iteration.
Failing to consume a matched prefix or changing the order of parts.
Self Check
Review questions before you submit
Uses each part start and length when decoding.
The substring end index is start plus length.
Retrieves substrings from the master string.
Append each retrieved substring in the original list order.
Uses the supplied findPart helper when encoding.
Do not replace the helper with a separate matching algorithm.
Advances past each encoded prefix.
Each findPart result has positive length; consume that many characters.
Practice Links