An unofficial guide to the Facebook Engineering Puzzles: Java

Quick start

Solve hoppity first regardless of what you may have been told to do.
Follow these instructions carefully. The robot has zero tolerance for error.
Your program must be compatible with Java 5. Developing with a later version requires care.
- You cannot use any of the new classes or methods. Consult the API specification early and often.
- In Java 5, a non-overriding method with an @Override annotation is an error.
- Compatibility mode will not help you figure out why the robot cannot build your code.
Use my antfile: build.xml. The robot’s requirements do not conform to Java conventions.
- Name your main class hoppity.
- Do not put any of your classes in a package.
- To reuse my antfile for other puzzles, change the keyword.
On Windows, save your source code and make/antfile with no byte-order mark (BOM). In Notepad, select encoding “ANSI”. In Notepad++, select encoding “UTF-8 without BOM”. No action is required in editors intended specifically for programming.
Read from the file specified as args[0], the first command-line argument. Open this file for reading only.
Write the unique correct sequence of bytes to the standard output stream (“the screen”) and terminate. Do not write to the standard error stream.
Attaching your source code and a make/antfile, send an email to 1051962371@fb.com with subject hoppity. Do not attach a digital signature.
You should receive a reply within an hour or so.
Sample solution: build.xml, hoppity.java

java.util.Scanner is handy for reading the input. Note, however, that one of the peaktraffic inputs triggers a known bug in the Java 5 version of this class.