Anyone heard of codility? (Automated Programming Assessment)

way2lazy2care · 2010-02-22T11:03:25

We had a discussion on testing programmers for interviews in here somewhere a couple days ago, and today I stumbled across codility. What it seems to do is that it will ask you a programming problem, and the user will write a piece of code in their in browser editor then submit it. The system will then grade based on different test cases and optimizations of the code. I took one to see what it was (you get 5 free tests). Lets you solve the problem in a bunch of languages. Pretty nifty. Wondering what people in the industry think about it/if they've heard of it. Wish they offered more than 5 free tests as it's a nice little way to brush up on languages I haven't used in a while. http://codility.com/

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Started by way2lazy2care February 20, 2010 04:13 PM

35 comments, last by janta 14 years, 8 months ago

Antheus

2,410

February 20, 2010 08:56 PM

Quote: Original post by nullsquared
Just something I found funny:

Funny how Java is sometimes tied or faster than C. Obviously, the 0.22 time is JVM startup.

Large pyramid is 0.268-0.220 = 0.48 vs. 0.56

And that is even without native compiler kicking in (1000/10000 calls of method).

M2tM

948

February 20, 2010 09:01 PM

Here was my solution (it is obvious I went for a more "fun" and less utilitarian approach to pad out some of the extra time I was given):

*EDIT: Solved the overflow thing. It got me the first time and I ended up with a 94. Seems I wasn't the only one. Kind of a kludge... Whatever.

#include <list>#include <algorithm>struct IsEquilibrium{   IsEquilibrium(long int tot, int &ind):total(tot),index(&ind){*index = -1;}   bool operator()(pair<long int, long int> element){      (*index)++;      return (element.first == (total - element.first - element.second));   }   long int total;   int *index;};struct Amounts{   Amounts():total(0),error(false){}   void operator()(const int &amount){      amounts.push_back(pair<long int, long int>(total, amount));      if((total + amount < total && amount > 0) || (total + amount > total && amount < 0)){         error = true;      }      total+=amount;   }   int getEquilibrium(){      if(error){return -1;}      int index;      if(find_if(amounts.begin(), amounts.end(), IsEquilibrium(total, index)) == amounts.end()){         index = -1;      }      return index;   }   list<pair<long int, long int> > amounts;   long int total;   bool error;};int equi ( const vector<int> &A ) {   Amounts totals;   return for_each(A.begin(), A.end(), totals).getEquilibrium();}

[Edited by - M2tM on February 21, 2010 7:01:34 AM]

_______________________"You're using a screwdriver to nail some glue to a ming vase. " -ToohrVyk

mattd

1,078

February 20, 2010 11:19 PM

Python for me too :)

def equi(A):    lhs, rhs = 0, sum(A)    for i, e in enumerate(A):        rhs -= e        if lhs == rhs:            return i        lhs += e    return -1

M2tM

948

February 21, 2010 07:40 AM

How about PHP?

function equi ( $A ) {    $total = array_sum($A);    foreach($A as $key => $value){        if(($accumulated) == ($total - $accumulated - $value)){            return $key;        }        $accumulated += $value;    }    return -1;}

And &#106avascript (for this one I just implemented the solution presented by SiCrane in &#106avascript) (this keeps putting in [] around literal 0's when I use lang="&#106avascript"...) <div class="source"><pre> function sum( A ) { var result = 0; for(var i = 0;i < A.length;i++) { result += A } return result } function equi ( A ) { var right = sum(A); var left = 0; for(var i = 0;i < A.length;i++){ right-=A; if(left==right){ return i; } left+=A; } return -1; } </pre></div>

_______________________"You're using a screwdriver to nail some glue to a ming vase. " -ToohrVyk

nullsquared

128

February 21, 2010 08:06 AM

Quote: Original post by Antheus
Funny how Java is sometimes tied or faster than C.

Logically, that doesn't make sense. The JVM is written in C++, therefore something written in Java can only be as fast or slower than the exact equivalent in C/C++.

Quote: Obviously, the 0.22 time is JVM startup.

That's not a bad point, though I'm willing to say that their timing method is not quite up to par.

Quote:
Large pyramid is 0.268-0.220 = 0.48 vs. 0.56

See above.

Quote: Original post by SiCrane
This was my Python attempt. It looks pretty similar to Sneftel's except that it doesn't special case the last iteration.
def equi ( A ):  a = 0  b = sum(A)  for i in range(len(A)):    b -= A    if a == b:      return i    a += A  return -1

If you look above, that was pretty much my exact first attempt, except that I special cased empty and size=1 arrays [smile] (which wasn't necessary, but it got my mind going [grin])

www.nullular.com

Sneftel

1,788

February 21, 2010 08:13 AM

Quote: Original post by nullsquared
Logically, that doesn't make sense. The JVM is written in C++, therefore something written in Java can only be as fast or slower than the exact equivalent in C/C++.

That's not how Java VMs have worked for years. Google "just-in-time compilation".

nullsquared

128

February 21, 2010 08:17 AM

In fact, notice how most of the measurements for the C version were 0s. The last one in C was either a fluke, or their Java measurements were inaccurate.

@ Sneftel: Not the point - the same code in Java won't JIT compile to something as efficient or more efficient than the same code in C. Though it'd be interesting to see proof that shows otherwise [smile].

www.nullular.com

Antheus

2,410

February 21, 2010 08:28 AM

Quote: Original post by nullsquared
In fact, notice how most of the measurements for the C version were 0s. The last one in C was either a fluke, or their Java measurements were inaccurate.

So you reject the reality and substitute your own? Your statement means that both Java and C version fluked on same test, and they were both pair-wise correct on every other test.

Quote: @ Sneftel: Not the point - the same code in Java won't JIT compile to something as efficient or more efficient than the same code in C. Though it'd be interesting to see proof that shows otherwise [smile].

Why not?

Since this is a trivial case, depending on how C code gets compiled, the Java version might put variables closer together, reducing number of cache misses. Just one or two cases as such and you've saved several hundred, perhaps even thousands of cycles.

Code hasn't been a bottleneck in a while now, memory is. And while it cannot be controlled, unless specifically managed in C, JVM might just result in slightly more optimal version, considering we're dealing with arrays, which Java can allocate in place, compared to List<> which requires instances of objects.

Quote: The JVM is written in C++, therefore something written in Java can only be as fast or slower than the exact equivalent in C/C++.

So C or C++ application can never be faster than something written in assembly?

Some assembly code can be faster than compiled C/C++ code.

BTW, do not underestimate JVM's design. When it comes to large application (1MLOC+), JVM will offer considerably better run-time characteristics than equivalent-effort C++ application precisely due to memory management. I mean this seriously, the micro overhead starts mattering surprisingly little above certain size, without even mentioning the difference in development time.

The biggest problem with Java is its legacy-ridden standard library and abysmal quality of third-party libraries. JVM however is fine, as demonstrated by JRuby, Clojure, Scala, etc... They are a whole different beast.

Sneftel

1,788

February 21, 2010 08:43 AM

Quote: Original post by nullsquared
@ Sneftel: Not the point - the same code in Java won't JIT compile to something as efficient or more efficient than the same code in C.

JIT-compiled code can potentially run faster than optimized precompiled C, due to the ability of the compiler to dynamically recompile portions of the code in response to dynamic analysis as well as the specific processor it's running on.

itachi

296

February 21, 2010 08:47 AM

Heh, that was fun.

This was my solution (C#):

int equi ( int[] A ) {         double totalSum = 0;         for (int i=0;i<A.Length;i++){        totalSum += A;    }         double currentSum = 0;         for (int i=0;i<A.Length;i++){             int current = A;        totalSum -= current;                 if (totalSum == currentSum) {            return i;        }        currentSum += current;    }         return -1;}

Time used: 12 minutes
Score: 100/100

Anyone heard of codility? (Automated Programming Assessment)

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Anyone heard of codility? (Automated Programming Assessment)

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