This is the only thing they really care about. You can just interrupt your process if you feel that you did not well as any successive steps will be a waste of time for you. This is the subject of Java programming test: Programming with low level array of bits or of array of strings. No ArrayList or collection is allowed. You have just to be a master with array shuffling. Like these: int[] anArray , String[] anArray Also master single ampersand ("&") "bit-wise AND" operator with no boolen arguments. And all shift operators. You should able to use Java as a "C" programmer, this is the stuff they seem to do with Java.