The ReadyForZero Programming Challenge

https://www.readyforzero.com/challenge

by ithayer • 15 years ago

45 56 15 years ago

readyforzero.com

wccrawford• 15 years ago

Oh, that first question looks tasty. I dunno what a 'ReadyForZero' is, but the challenge could be fun.

DanielStraight3• 15 years ago

I don't usually do these challenges, but this one was pretty fun. It's three problems long. Took me about 30 minutes.

kevinholesh• 15 years ago

From the source of the website: ""

It was worth a shot.

gjm11• 15 years ago

Three problems, algorithm-centric, each solvable with (some intelligent thought and) a few lines of (say) Python. Unsurprisingly, the payoff is "we're hiring; please send us your resume".

ReadyForZero appears to be a company that helps people get out of credit card debt by tracking what you owe to whom and recommending what to pay off in what order. They just got Series A funding.

troyk• 15 years ago

Could that be a booger on the 1 key (numeric keypad)?

nottodayy2• 15 years ago

Reading the first problem, I think I am not ready for zero, it seems that the first problem is not well described.

zheng• 15 years ago

You are looking for a sequence of 5 characters that differ by one character, but are otherwise identical (order matters). For example, an answer would be something like '89^hf' and '8z^hf'

nottodayy2• 15 years ago

Thanks, order matters that's what I missed.

gmaslov• 15 years ago

These are very similar to (and easier than most of) the Project Euler problems. http://projecteuler.net/ -- Highly recommended for everyone.

ithayer8• 15 years ago

If anyone wants the hard version, let me know (you can upvote this comment)

drdo7• 15 years ago

Wasn't hard. The problems could be better explained, for example in the second one they should clarify that the binary tree is balanced and that each node is one character.

noglorp3• 15 years ago

> binary tree is balanced and that each node is one character

I found that pretty intuitive given they tell us it is a tree with 2^n-1 nodes, and that this is then umber of characters in the text file.

What I'm wondering about is what the '=' pad character means in the context of non-valid base64 (i.e. isn't it the same as the 'A' character - a null?)

ithayer8• 15 years ago

you're right - we should explain that it's balanced.

drdo7• 15 years ago

One quickly realises that you must mean a balanced tree, since otherwise there would be no unique solution, but it would still be nice if it was explicit in the text.

noglorp3• 15 years ago

Any comment in regard to my question above? At present, question 2 has serious ambiguity as to how one should interpret the data. Clearly each character represents one node, but again, there is no clear procedure for converting values. Padding makes no sense in this context.

Can you clarify?

leif• 15 years ago

yeah I thought it was base64 and that was annoying

amalcon2• 15 years ago

The most difficult part was figuring out unspecified things in the problems. Generally I had to use my intuition about "otherwise this would be either impossible or too easy" to get the right answer.

The first problem should be more explicit about the nature of the difference: a "typo" or non-shared could reasonably be an omission of a character, which would mean that the position of the unknown character does not matter. This weaker problem has more than one correct answer for the given input data. Better to call it a "corrupted byte" or somesuch.

It should be explicitly stated that the tree is balanced in the second problem. It should also state that each node contains exactly one character or that all nodes have nonempty payload (you can figure out either of those pieces of information from the other one).

The third problem should specify that it's looking for a strict partition. Contiguous is not a strong enough requirement. As written, I can have as many "contiguous subsequences" of zero elements as I want located anywhere in the string.

I particularly like the third as a teaching problem, and I might have to use it sometime. It's pretty simple, not overly reliant on programming concepts, and the "clever" solution is both faster and easier to implement than the brute-force try-everything solution.

ithayer8• 15 years ago

Very good points. The computer screen wasn't that large so I tried to keep the descriptions short. :)

ibdknox• 15 years ago

Given that the point of this is to have fun and also tease out people worth hiring, having ambiguity in the problems is a good thing I think. Rarely is a real technical problem so clearly and obviously defined. So requiring a bit of thought and intuition might prove to be a good filter :)

leon_• 15 years ago

> Are you ready to get out of credit card debt? > ReadyForZero is a free online financial tool that lets you track your credit card debt ...

what is this? some kind of a sick SEO experiment? flagged for spam.

ithayer8• 15 years ago

Not an SEO experiment - trying to hire smrt people!

llimllib3• 15 years ago

My answers in 31 lines of code: https://gist.github.com/1025860

I am either misreading the third problem's description, or I have a bug I can't for the life of me see, because the answer my program puts out is not accepted.

DanielStraight3• 15 years ago

The third problem is looking to partition the entire sequence of numbers into contiguous subsequences, all of which add up to the same sum. In other words, if the list were 23415, you subsequences could be 23, 41 and 5, all equaling 5. But the subsequences have to use up the entire string and they can't overlap.

hugh33• 15 years ago

Did anyone else do that one without writing any code?

llimllib3• 15 years ago

They can't overlap! I don't think the problem specifies that?

You have to interpret "break up" to mean "non-overlapping" to claim that the problem means what you're saying it means; I found 341 "contiguous subsequences such that the sums of each of the subsequences are equal", but they overlap.

(If you had said "partition" I suspect I would have got what you meant)

apaprocki• 15 years ago

> #pip install python-levenshtein > from Levenshtein import distance

That doesn't seem in the spirit of the challenge.

ithayer8• 15 years ago

Can you do it in linear time in the length of the input?

llimllib3• 15 years ago

Why? It's not hard to write a quick and dirty levenshtein function, but when google gets it for me in 1 minute, why do it?

edit: just for fun, as a one-liner:

    def levenshtein(a,b): return sum(x!=y for x,y in zip(a, b))

edit 2: and just to clarify, I know this fails if the lengths of the input strings differ, they were guaranteed to be equal in my code.

abofh• 15 years ago

Meh, it killed an hour or two that needed to suffer.

genesiss2• 15 years ago

I enjoyed solving these. Last one is cool, but hint is too obvious ;>

drdaeman• 15 years ago

When one has cookies disabled (and those days I believe everyone should) it throws Django error page:

> Forbidden (403)

> CSRF verification failed. Request aborted.

They should've checked that cookie exists. Or, better, not rely on cookies.

ithayer8• 15 years ago

Thanks for pointing that out. Yes, we could have checked every single corner case, but our job is to build financial software, not programming challenges, so we did it quick and dirty :)

decultured• 15 years ago

Fun challenge, but not too difficult. The largest challenge was making the intuitive leaps to discover the missing information in the questions, especially for problem two. A bit of trial and error, and a few lines of Python made for quick testing of those assumptions.

pom• 15 years ago

That was a fun before-breakfast warmup; the input was always short enough that a simple, brute-force approach would usually work. The problem statements could have been made a little bit clearer though.

And what's up with the green-on-black Mac screen?!

EDIT: my solutions (using Node.js) https://github.com/julienq/incubator/tree/master/misc/readyf...

sokolski• 15 years ago

My solutions: https://gist.github.com/1026309 Didn't really stop and think on the first one for too long, so it's a bit messy. Overall it's quite easy but not trivial. Knowing the length of the challege at the beginnig wold be nice though.

dhugiaskmak• 15 years ago

Here are my solutions for #1 and #3. I cheated on #2 just like everyone else.

https://gist.github.com/1026404

owenjones• 15 years ago

Hello could someone help me with problem 2? I believe I am splitting the string correctly, 1 2 4 8 16 ... 512 = 1023 total chars/nodes, but when I add the integers of the last line (aka the leaves) I get the wrong result.

https://gist.github.com/1029356

Thanks.

ralphc2• 15 years ago

Solutions in Clojure https://gist.github.com/1033605

I "cheated" on the third one in that I read the discussion here which helped clarify the problem, non-overlapping, etc.

ralphc2• 15 years ago

I figured out a better challenge 1 with combinatorics, also figured out non-anonymous gists https://gist.github.com/1041697

The ReadyForZero Programming Challenge

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