Author 
Message 
Kikifax
Joined: 18 Nov 2008 Posts: 2


Snake Arithmetic 

Hey,
I have a very convincing looking solution for this challenge,
but it isnt accepted.
Just wondering if the challenge might be broken (ok, guess thats a remote hope)
or if that very convincing looking solution is simply wrong.
Thanks for any input.


Wed Nov 26, 2008 3:24 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182 Location: HkRkoz al KuwaiT 2019 HaCkEr 101 



Your answer must be very exact. Depending on your method of calculation, you can get approximations which are close, but not close enough.
If you've simplifed the snake arithmetic into a solvable summation, it will still require some gymnastics to do this summation with enough precision.
If you've simplified the summation down to a basic equation, this could be easily done with no real gymnastics.


Wed Nov 26, 2008 6:39 am 


therethinker
Joined: 28 Mar 2008 Posts: 144 Location: #hacker.org on Freenode 



Wait, there was precision? Its python, and all the numbers are integers, so there should be no decimals, right?
As MerickOWA noted, this can be greatly simplified. At least as far as I got, it still would require a computer to solve, but its loads simpler/quicker than the origional problem.


Wed Nov 26, 2008 8:06 pm 


cyberwoozle
Joined: 07 Nov 2008 Posts: 60 Location: Germany 



I'm short before getting crazy!
What i found (and still believe) is, that it's a linear, steadily increasing funtion. Correct?
I simplified it down to a solution, which doesn't even require a calculator  i think, it can be done with a piece of paper and a pen.
So what's the trick with the precision


Wed Nov 26, 2008 10:29 pm 


gfoot
Joined: 05 Sep 2007 Posts: 269 Location: Brighton, UK 



Precision was an issue for me  it depends how you treat the division in the outer expression you're simplifying. But I didn't solve this challenge very well... I stopped thinking about it too early and just let a computer churn on it.


Wed Nov 26, 2008 11:16 pm 


therethinker
Joined: 28 Mar 2008 Posts: 144 Location: #hacker.org on Freenode 



Its *definitely* not linear. Plot out a graph for like b = 0 to b = 100. (I used python then imported into a spreadsheet program)
Be careful with precision though, python will round since they're ints. Add a ".0" to one of the constants: floats are infective.


Thu Nov 27, 2008 12:56 am 


Grammaton
Joined: 04 Nov 2008 Posts: 9 Location: Bavaria, Germany 



I have the same problem. i analysed the first values, and programmed the iteration sequence. I did it on some diffrent way, with math (pen and paper) and with a calculation loop, i am always getting the same result. "...999...". I checked it more times, but i cannot find the problem. :/


Sun Nov 30, 2008 9:44 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182 Location: HkRkoz al KuwaiT 2019 HaCkEr 101 



You've got to be leaving something out of the equation then.
These values get very large very quick. Theres no way to directly calculate N(4*b) or D(4*b) out as integers for any sufficiently large value of b without a very very large amount of memory and time. This is the problem with all recursive functions.
You must simplify it. You can simplify it into an iterative equation which uses the calculation from the previous step to calculate it for the next step, and then repeat 1000000000000 times. Or, you must actually come up with an equation which describes the number the iterative / recursive equations are trying to give you.


Mon Dec 01, 2008 1:35 am 


osterlaus
Joined: 02 Nov 2008 Posts: 20






Your answer must be very exact. Depending on your method of calculation, you can get approximations which are close, but not close enough. 
Sorry, but I don't get that. How could there be precision? If I call this division for, lets say, b=100, I get a number without decimals. Same with b=1000...


Fri Dec 26, 2008 7:50 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182 Location: HkRkoz al KuwaiT 2019 HaCkEr 101 



I don't think this is too much of a give away, but this number goes on forever, larger values of b only return more of the number.
You don't get the decimals returned because all of the math is done with integer arithmetic. The division between N(4*b)*b and D(4*b) drops any remainder.


Fri Dec 26, 2008 5:45 pm 


m!nus
Joined: 28 Jul 2007 Posts: 202 Location: Germany 



I like maths, but I'm not so good with this stuff (because I've never done anything alike (recursive)).
So, can someone lend me a supercomputer?


Fri Dec 26, 2008 9:08 pm 


honze
Joined: 03 Nov 2008 Posts: 6 Location: Munich, Germany 



I figured out, what python means with "and" and "or".
I took the two recursive functions and transformed them into nonrecursive functions.
I found an expression, that represents the (N(b*4)*b)/D(b*4) as a sum.
I found an expression, that represents the sum DIRECT. So I just have to type a few characters into python... And this answer is still wrong. I crosschecked my mathematical transformations with a math software. I even get the same result with the online python interpreter...
So, where I am wrong?


Fri Mar 05, 2010 10:16 pm 


cutter
Joined: 12 Jan 2009 Posts: 17




try adding 1 to your solution


Sat Mar 06, 2010 4:20 pm 


honze
Joined: 03 Nov 2008 Posts: 6 Location: Munich, Germany 



I added the 1 already to my solution. Didn't forget that.
Maybe there is an inaccuracy in the representation.
There two possibilities to display the number:
a) x.xxxxxxxxxxxe+xx
b) xxxxxxxxxxxxx.xxx


Mon Mar 08, 2010 7:29 pm 


michuber
Joined: 26 Oct 2008 Posts: 57






a) x.xxxxxxxxxxxe+xx
b) xxxxxxxxxxxxx.xxx 
c) xxxxxxxxxxxxx


Tue Mar 09, 2010 7:25 am 


