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I have been going through the Java interview questions asked by my company and came across one that I can't seem to find the solution.

Here is the question:

Please write a method (function) accepting as single parameter a string and reversing the order of the words in this string.

The " " is the word separator and any other char is considered as being part of a word. In order to simplify, please consider that there is always one space between the words.

Important - You are NOT allowed to use other strings or arrays or other data structures containing several elements - just plain atomic variables such as integers, chars etc.

Also, it is not allowed to use any other language specific string function other than the function giving you the length of the string.

Expected result:

"hello my beautiful world" -> "world beautiful my hello"

So, I can't use: chars[], str.split(), str.charAt(), str.substring(), StringBuilder, another declaration of String.

Should I use recursion to do it?

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    Yes, you should recurse. Commented May 18, 2016 at 12:10
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    Side note: this seems to be one of the questions where I am asking: "and you are sure that 'knowing' how to do this ... makes up a good programmer?" Besides, if that puzzle by your company; somebody in your company should have the solution to it, right? (as I agree with the others; given those requirements; I don't see a way to solve this). Or are you saying that somebody put up that question; but nobody knows the answer to it? Commented May 18, 2016 at 12:17
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    Another question in the series of dumb interview questions. "Show us what you know, but you can't use what you know." When is this type of problem EVER going to arise in day-to-day work? Commented May 18, 2016 at 12:20
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    Create a web application that reverses a String, then send your String parameter to its URL, and print the response result. Runtime.exec is probably another overkilling way of doing this. :) Commented May 18, 2016 at 12:28
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    @TobiasBrösamle you have a point there (what good is a String if you cannot access its data?). But OP specifically said that charAt(int) is not allowed, Commented May 18, 2016 at 12:30

2 Answers 2

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Since, String is Immutable and uses encapsulation,

There is no solution to your problem. You can't update the values directly, no setters are available and without the access to the getters (since you can only use .length), you can't read the value.

So, I would suggest to respond that Immutability and encapsulation prevent you from doing so.

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In real life as a software engineer, you'll sometimes be asked to do things that are technically impossible or even nonsensical. Sometimes the person asking will be someone important like your boss or a big customer.

If someone actually asks you this interview question, then you're in one of those situations. That makes this question pretty interesting, and you might want to figure out what the best way to answer really is.

If someone asked me, this is how I would answer, and as an interviewer, this is the kind of answer I would award the most points for:

1) Explain how it's technically impossible to meet the requirements, but do it without making me feel stupid. This shows diplomacy.

2) Figure out what I really want. In this case, the interviewer probably wants to see if you know how to reverse the words in a string using low-level operations. This is a perfectly reasonable C language question, for example. Figuring out what the interviewer really wants shows experience and judgement.

3) Provide an answer that gives me what I want. Write this method in Java, but take a StringBuilder instead of a string, and call only length(), charAt(), and setCharAt(). This shows the expertise that the interviewer wants to see.

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