Discussion on:

Test developer candidates with Codility

These tests are necessary, but should not be put before a phone interview. The interview process is a two way street. The candidate wants to know what you really need. Over the years I have had many short and sweet (under 3 minute) phone interviews. At that point I was able to say, "Thank you. I'm not the guy you're looking for, and here is why." To do that, I had to talk, yes talk, to the person doing the hiring. Not the recruiter, not a test.

Requiring a half hour investment up front (4x30 minute questions is half an hour for a qualified candidate) eliminates candidates who budget their time. Take a test and learn nothing about the position, or go outside and play? Easy choice.

Supports, per their website: Java, C++, C, C#, Python, PHP, Ruby, JavaScript, Pascal, Objective-C, Perl, VB.NET, Lua, SQL

Pascal? There are some folks who will state, quite forcefully, that Pascal was never meant for the real world.

No BASIC, Fortran, CoBOL, APL, Ada, PL/1, etc? There is much so-called legacy code in need of support.

Care to share some of the easy, or medium, questions?

I did their demo assignment, and it was indeed a nice challenge. It took me a couple of minutes to get used to the interface, the way to use the tests, and the response. I am quicte used to Eclipse and I am very spoiled by the auto complete and other handy little things. Obviously, none of this is available, you have to do it all alone. But that is not a bad thing! For a next hire I will defenitely use this product.

Software development in the real world requires many skills: defining, documenting, and approving requirements; designing user interface; designing software; integrating software into existing system; writing software; testing software; debugging software. Writing software is often a small part of the overall project. In my last project, writing code took 1 week out of a 3 month project. Yes, knowing how to write code is important. Focusing on writing code when hiring a software developer may not get the best candidate.

A zero-indexed array A consisting of N integers is given. An equilibrium index of this array is any integer P such that 0 P N and the sum of elements of lower indices is equal to the sum of elements of higher indices, i.e.

A[0] + A[1] + ... + A[P1] = A[P+1] + ... + A[N2] + A[N1].

Sum of zero elements is assumed to be equal to 0. This can happen if P = 0 or if P = N1.

For example, consider the following array A consisting of N = 7 elements:

A[0] = -7 A[1] = 1 A[2] = 5
A[3] = 2 A[4] = -4 A[5] = 3
A[6] = 0

P = 3 is an equilibrium index of this array, because:

A[0] + A[1] + A[2] = A[4] + A[5] + A[6]

P = 6 is also an equilibrium index, because:

A[0] + A[1] + A[2] + A[3] + A[4] + A[5] = 0

and there are no elements with indices greater than 6.

P = 7 is not an equilibrium index, because it does not fulfill the condition 0 P N.

Write a function

Private Function equi ( A As Integer() ) as Integer

that, given a zero-indexed array A consisting of N integers, returns any of its equilibrium indices. The function should return 1 if no equilibrium index exists.

Assume that:

N is an integer within the range [0..10,000,000];
each element of array A is an integer within the range [2,147,483,648..2,147,483,647].

For example, given array A such that

A[0] = -7 A[1] = 1 A[2] = 5
A[3] = 2 A[4] = -4 A[5] = 3
A[6] = 0

the function may return 3 or 6, as explained above.

Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).

Elements of input arrays can be modified.


My eyes glossed over trying to read this....
I suppose my first problem is I don't know what an equilibrium indices is.

I guess I suck at programming. Or probably reading comprehension.

I tried this

try
return 6
catch
return 3
end try

I figured it should be right at least half the time, but it gave me a zero

Try?
There is no "try", there is "DO WHILE SUCCESSFUL", or "REPEAT UNTIL FAIL"

Do

loop until 1= 2

Yay! If I put that it, I wonder if the web service would hang trying to get a result from that.

My "try humor".

Unfortunately those answers are only right for the example and the actual answer can be in the range [2,147,483,648..2,147,483,647]. But if that try catch loop works you may have a way to hack through many of the questions.

You need to find the array index where the sum of all the elements before it matches the sum of all the elements after it.
If A[0] + A[1] + A[2] = A[4] + A[5] +A[6] the answer is 3

I'll have to think about that....


-Edit
This is what I figured out, I don't like that it doesn't include the current index. I think the real answer is 5, but to get 3 I exclude the current index in the math.
I wrote in in VB6 just cause I had the IDE open at the time

Option Explicit

Private Sub Form_Load()
Dim aTest(0 To 6) As Double
Dim i As Double
Dim iAnswer As Double

aTest(0) = -7
aTest(1) = 1
aTest(2) = 5
aTest(3) = 2
aTest(4) = -4
aTest(5) = 3
aTest(6) = 0

iAnswer = 1
For i = LBound(aTest) + 1 To UBound(aTest) - 1 Step 1
If SumArray(aTest, LBound(aTest), i - 1) = SumArray(aTest, i + 1, UBound(aTest)) Then
iAnswer = i
Exit For
End If
Next i

Call MsgBox(iAnswer)


End Sub

Private Function SumArray(ByRef arr() As Double, iFromIndex As Double, iToIndex As Double) As Double
Dim i As Double
Dim sum As Double
For i = iFromIndex To iToIndex Step 1
sum = sum + arr(i)
Next i
SumArray = sum
End Function

really fits into single recursive function. It's like imaginary slider moving from the start to the end of an array. We have 2 sums - Before and After the slider index. Every time slider moves, value of its element is added to the Before sum and is taken from After. Naturally, at the start Before = 0, After = sum of all the elements. That the only time we need to calculate the sum of number of the elements. After that would be only single subtraction/addition. Function keeps calling itself with parameters of slider index and Before and After sums. The function compares sums, increments number of equilibrium indices, if they're equal, and adds slider index value to resulting collection, again, if satisfied. Slider index is incremented, Before and After sums are updated as well. Then the function is called again from itself. Condition of leaving recursion is when slider index reaches the end of an array.

You get points for geek factor, but lose points for the inherent problem recursion has, you risk running out of stack space.

yes, of course - depending on array size. But we can easily convert it to linear sequence with the same params set - no big deal...

Can you write some code for it? I'd like to see what you mean.

... some of the questions were not good, because it is easy to get hung up on the question itself... this is an example of one such question.

J.Ja

Hello,

I am one that has been victim to this thing. Even after this discussion this test was still used in a hiring process I recently went through. Do these questions seem like entry level developer questions? I have an associates in Computer Information Systems and have not seen anything similar to this before the test.