HackerRank aims to build a fun place for programmers to hang out | Hacker News Reader

HackerRank aims to build a fun place for programmers to hang out

hackerrank.com

39 pointsrvivek54 comments

A few things:

* I'm having issues with the terminal where what I type is not always on the bottom line. Also, the up/down arrows for getting command history don't always show what I would expect and I get latency fairly frequently.

Also spoiler here's an algorithm that will let you win every time where it is possible to win. I debated a bit about posting this, but if I didn't I'm sure somebody else would.

1. If number is divisible by 6, do not play since you'll always lose.

2. If the number is less than 6, do not play since it doesn't allow you to take them all in the first move, despite what the instructions suggest.

3. Otherwise, your first pick should be a number that takes the remaining number to a multiple of six (see rule #1). Then, you should look at what number the computer picks and subtract it from six when you pick your number.

Getting to the top of the leaderboard is dependent on understanding this and how much time you're willing to spend playing.

Or you could write a bot that plays the game for you. Then getting to the top of the leaderboard depends on who started their bot first and the quality of bots' network connections.

I was about to post this exact thing. Its easy enough to figure out if you watch the computer play. Using this its possible to win every single game as long as the number you start with isn't divisible by 6.

:) This was just a teaser page/warmup puzzle for fun. Thanks for trying out!

Was able to sign up, but the challenge totally failed on me.

First it seemed to not be taking any input, and let me enter about 10 different numbers without response. Then, it showed me the back and forth between me and the computer for about half of those numbers, but the total never changed after that.

The command is challenge <number>

Yes, I started the challenge. My problems were encountered during the game itself. It stopped working correctly.

The game worked fine for me, just double check "challenge 1" since it asks for a range between "1 and 0"

A few observations:

- If you start <= 6, you will always lose, since you have to choose 1 less than the starting number.

- Whoever gets 6 on their turn will always lose.

- If you start between 7 and 11, you'll always win.

- If you start at 12 or higher, you'll usually lose, since the computer will try to get you to 6.

Still fun for a few minutes atleast. No idea how people are winning 20+ games.

Some of them write a 'script' ;)

> If you start at 12 or higher, you'll usually lose, since the computer will try to get you to 6.

Ah, but you can also try to get the computer to 6 ;).

>No idea how people are winning 20+ games.

I won over 20 games by just spending a few minutes manually running the algorithm described elsewhere here and I imagine anyone who hasn't won hundreds or thousands of games probably did the same. (If you're going to write a bot, might as well let it run for awhile and see if you can max out the leaderboard.)

All you have to do is hand the computer a number that is divisible by 6 each time.

If you start with 61 pick one and the computer has 60, say it picks 4 and you have 56 pick 2 so you hand it 54. Repeat until you win.

The CLI seems to get into an inconsistent state easily in Chrome, only fixed by reloading the page. I'm sure I know how to win the candy challenge based on the english description of the rules, but I can't make any sense of the output.

    recursive@hackerrank:~$  challenge 1
    Playing a game for N: 1
    Please provide a number between 1 or 0.
    How many candies you want to pick?:

At this point, I get stuck in a loop that I've only been able to get out of with f5.

I am a novice programmer and I am always put off websites that rank users (and programming competitions for that matter). Avoiding the competition seems better than putting my relatively crappy code out there for all to see.

Would more seasoned people out there agree that a clean slate is better than a low ranking on sites like InterviewStreet (or HackerRank if it gets big)?

Hi Ayla, we want to build something that has fun stuff catering to different set of programmers (hackers/programming contest enthusiasts/functional programmers, etc.) Whether it's for pride or for learning new things, we want to leave it to the user.

I agree, as someone that's still just getting my toes wet, as soon as I saw the leaderboard aspect I was like "Ah, this isn't going to be my type of place.."

Well, I was trying to avoid spoilers, but since jaredsohn has already sailed that boat out to sea...

How do you script something like this? I tried looking at the source and then using the chrome console to input jQuery commands, but something really weird happened. I could replace just about any element on the screen except the one that mattered!

I could type "challenge 8" into the console and then running a $('tester').text() would return "challenge 8" as expected. But $('tester').text('challenge 9') wouldn't update the screen. I tried for a good hour to find a way to update the text in that element, with no luck (short of removing the whole thing from the dom).

(see http://postimage.org/image/c3xkrg8y3/ )

Also how do you send a carriage return? Inserting a newline didn't seem to do the trick. Anyone? As much as I love a challenge, beating my head against this one issue doesn't yield much education / time spent.

If you look at the JavaScript, you can see that it actually expects a keystroke for the Enter key.

I'm not familiar with sending keystrokes in JavaScript (from some brief searching I think it is possible; I just don't know the best practice), but for something like this, you could just do it at the operating system level. A long time ago I automated an annoying user interface for a program we had to use at work by writing some vbscript that changes windows and does a combination of sendkeys and sleep.

Unfortunately, just sending keystrokes isn't very robust since it isn't reading what is going on in the UI and if something random happens (the site behaves other than expected, you touch a key / move the mouse, a scheduled program runs, etc) the script could get out of sync. Fortunately, the consequences of an error are so low here that such a solution would be good enough.

Vivek, Cannot access at the bank. Contacted friends at other banks. Same story :( So some 1 million plus corporate programmers don't have access to your website. Here's the message I get on Internet Explorer.

--------- 403 Forbidden

This Web site is blocked: http://hackerrank.com/ As part of our ongoing effort to protect the bank and its information, the Web site you are trying to reach is blocked because it is classified in a category the bank considers to have certain risks. The bank blocks access to a number of Web site classifications including but not limited to Web mail sites, Personal Network Storage, and other categories to comply with regulations, protect customer and company information, and to be consistent with industry standards and practices.

This Web site is categorized as Games. ---------

I'd say that's probably a good thing considering the passwords were being transmitted in the clear[1]. To me this would seem a huge liability to be accessible by bank employees.

[1]https://gist.github.com/3020091/

We're getting https certificate.

imho the reason is the name. If news.ycombinator.com was called hackernews.com, it would be blocked in 15 seconds flat. That's corporate america for you.

Hackerne.ws points to the same IP address as news.ycombinator.com. Is the former blocked but the latter allowed?

Am I missing something? I type signup myemail myusername and I am then prompted for a password which seems to refuse any input or at least not alert me of submission.

The signup is broken, there is a 'login undefined property' exception.

Hope this will be fix soon, cool idea

Sorry, it's fixed. Can you try now?

I am a very novice programmer, but this challenge seems impossible. It asks "Please provide a number between 1 or -1". That isn't even English. Do you mean between 1 and -1? Any number entered just results in the same "Please provide a number between 1 or -1".

Did you not test this at all before promoting it? I am brand new to programming and even I know that testing is important.

Please use challenge <number> where number is >=5. Updating the problem text as well as the code

The error is when the argument to the `challenge` command is anything other than a number. Try `challenge monkey`. It then accepts zero for N, and the computer always picks a positive number.

Resulting in a negative.

I most certainly enjoyed that! Was nice to find the apply command after poking around in the help.

  == apply: Apply to join our awesome team.
  Usage: apply <a profile url> <why do you want to apply>

Does it have anything to do with my mad skillz in solving the puzzle perhaps? ;-)

This looks cool. But I'm getting a javascript error when trying to sign up.

TypeError: Cannot call method 'toLowerCase' of undefined [http://www.hackerrank.com/assets/application-18e8ea124a72677...]

very sorry about it. Can you try now?

Works now. Very cool, thanks!

And just found a bug. I started from 2000 and it got stuck at 378. It is miscalculating and thus going into an infinite loop. http://paste.ubuntu.com/1067434/ I mean come on, mathematical miscalculation for a game like this?

The algorithm is obviously pretty easy, as has been demonstrated...

but I can't believe I just spent 20 minutes trying to come up with a scripted solution. Nerd sniped again!

http://xkcd.com/356/

Congrats! There are 5 "scripted" solution till now.

So maybe I just fail, but I attempted to sign up, typed in the command and then it asked for a password. I assumed this was to make up a password, so I tried that, and it didn't let me enter. Is this a you have to know a password to sign up thing?

Sorry about it. Can you try now? It's fixed. A js error

Works now. Thanks.

I signed up, but it didn't appear to accept my password, presumably to the aforementioned JS bug, but trying to sign up again afterword tells me that my email is taken and won't log me in.

Is there a login link I can visit?

I'm going crazy or should I not have won here?

Playing a game for N: 10 Your move: '4'. Computer's move: '1'. Remaining candies: '5' Please provide a number between 1 or 5. Your move: '5'. Computer's move: '5'. Sorry! You lost the game.

I made the same moves and it said I won.

hey passwords are being sent plaintext (https://gist.github.com/3020091/). be careful if you signup/when you log in. use a password you don't care about, or use a throwaway.

Ha! I attempted this yesterday, after I saw the article in TC. It was a really fun challenge! Good job guys! Hope I didn't cost you a lot of money.. by my estimates i sent you something close to like a million requests .. give or take.

You guys rock !!!

I also write new bot by python for hackerrank challenge. Check out my code at https://github.com/kiennt/hackerrank-bot

Happy hacking :)

Thanks soo much for posting your code. Just starting out with python and it's nice to be able to learn from someone else's exploits.

There's a bug. The cursor sometimes shows up above the current prompt line and I'm not able to type. Clicking on the prompt will just bring it back for a second and then it goes up again.

$ Playing a game for N: 8 $ Your move: '2'. Computer's move: '2'. Remaining candies: '4' $ Congrats! You won the game. Now go ahead and play for more candies. Enjoy :)

Can you give solutions after the week is up? I really want to become a better programmer and I think this would really help me learn.

Yes, we'll be putting it up. Stay tuned. Thanks for trying

"Username can only contain characters, numbers and underscore." _RegEx_ doesn't work :(

I'm getting a whole mess of "You can't play that game!" errors on legitimate moves.

I am getting various errors - there are 4 remaining candies. I take 4. now there are 6 remaining candies...something is wrong.

Awesome stuff man...looking fwd to more challenges.

I must say, this 'challenge' is a creative idea.

However, not to be a wet blanket, but it's rather simple to construct a winning algorithm, particularly if you can both choose the same starting number and always go first (and choose the same starting number multiple times). If I had a few extra minutes at work right now, I'd take a stab at it.

...That is, unless that's the entire point?

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