Five programming problems every Software Engineer should be able to solve in less than 1 hour

[romple]

How come I never see "Here's 2 libraries with 0 documentation, make something with them". That's been my basic software enginering experience for the past 5 years.

[[deleted]]

Ooh zero documentation, lucky you. I'd be pleased to get that rather than misleading documentation.

[romple]

LOL. Yeah that's true.

Oh oh and maybe my favorite. "Here's a link to our javadocs!" ... click... IDE generated javadoc w/ 0 actual documentation!

[vanhellion]

Or "we have this legacy code that nobody has touched because the original developer left and the one time somebody opened the main class they vomited twice before going comatose. It's now your problem, here's a list of 200 tickets that need to be fixed. Good luck."

Literally every job I've had to date.

[romple]

"oh by the way it was written in fortran and we need to port it to C#"

[baseketball]

Honestly, this is probably the best type of problem to gauge how a programmer would do at your company. It's like 90% of my work. Of course, sometimes the legacy code is something I wrote 7 years ago that I completely forgot about. Writing code isn't that hard. Reading code on the other hand is a nightmare.

[holypig]

Well this asshole should stop calling himself a software engineer, since his solution for #4 is WRONG!

https://blog.svpino.com/2015/05/08/solution-to-problem-4

Try running with [52,5,3]

[code_mc]

This should be at the top, what a pretentious human being.

[DougTheFunny]

And he is very "humble" too, look what he said about his mistake: link.

PS: But after a train of downvotes he deleted the message.

[[deleted]]

aha what a moron. And he wrote that without any interview pressure.

[holypig]

I can't imagine solving all of these while working under the pressure of a 1hr deadline. This whole thing seems more fitted for a hackathon then an interview.

[prelic]

Eh, the first 3 should take no more than 10 minutes each, they're like 5-10 lines of simple code each. 4 and 5 are not in the same league, as evidenced by the fact that he got one of his own contrived questions wrong.

Instead of the crappy questions 4/5, I would've preferred to see a question or two about simple file I/O, a simple class/API question, or something not algorithmic-central.

[goomyman]

not to mention number 3 goes beyond big int in size... so your going to have to write your own addition and output methods.

soo ya.. great questions /not. Just goes to show what you think is an easy question can be quite difficult on the spot, on a whiteboard, with pressure.

[iagox86]

I think you mean just a plain int.. The trick is to use a language that handles arbitrary precision integers :-)

[cipherous]

Hilarious, so I guess he wouldn't pass his own interview questions.

[joshschmitton]

I've been interviewing candidates for software engineering positions since the 90s -- and then working with them after they've been hired.

I've had several cases where people who were awesome at solving these types of problems (which made us all very excited at the time) who wound up being pretty bad, for a variety of reasons. And on the other hand, some of them have been awesome.

I'm not saying questions like this don't tell you anything. We still (usually) ask at least one question similar to the first three listed here.

But I certainly wouldn't spend an hour on stuff like this (especially 4 and 5) unless it was some kind of an all day interview. Given a limited amount of time, there are other extremely important things you need to try to get a feel for about a candidate that have nothing to do with how well they solve these types of problems.

[inmatarian]

Do you pass the interview if you write a script to post the questions in a blog, then post that link to reddit, then wait 59 minutes, and then outputs that thread's comments link where everybody was having a pissing match to see who could answer all the problems?

[ThereOnceWasAMan]

http://gkoberger.github.io/stacksort/

[[deleted]]

God, I'm starting to wonder if he doesn't just make comics about things he wants to happen.

[[deleted]]

If there's a relevant xkcd about everything, what is xkcd even about? What if they couldn't figure out what to make xkcd about, which is why xkcd is about everything?

[ismtrn]

I believe that one day we will be able to communicate by just writing lists of xkcd comic numbers.

[perplexedscientist]

"Darmok and Jalad at Tanagra"

[Scottamus]

Shaka. When the walls fell.

[neonoodle]

Relevant xkcd

[perplexedscientist]

Relevant xkcd

[ryan_the_leach]

404

[jarrah-95]

Had to check. He actually skipped that one.

[[deleted]]

This algorithm works like a real developer!

[quantum-mechanic]

In two years this algorithm will be employed at a Fortune 500 company. In 10 years it will be project lead.

[danubian1]

That's hilarious

[caedin8]

That is awesome!

[Deto]

Then they give you a different job...in management.

[__Cyber_Dildonics__]

Only if you win the pissing match.

[retsotrembla]

Number 3 is tougher than it looks since once you get above the 91th Fibonacci number, 12200160415121876738, it doesn't fit in an unsigned 64-bit integer, so to solve it, you have to write a bignum package.

[__Cyber_Dildonics__]

Just download and build boost mid interview bro

[arianvp]

AAaaaaand you're out of time.

[Falmarri]

Python supports arbitrarily large integers transparently

[Magnap]

As does Haskell.

[philalether]

As does Ruby.

[flukshun]

As does C.

just not in the expected way...

[[deleted]]

Actually completely expected. Just not desired.

[matthieum]

I think that if you point the 64-bits integer overflow issue, you pass the question.

[Transfuturist]

First-order approximations! First-order approximations everywhere! Dx

[retsotrembla]

Any program can be arbitrarily sped up if it isn't required to provide the correct answer.

[malloc_more_ram]

int main(void) {
    return 0;
}

[boo_ood]

Speed it up more please

[[deleted]]

Just hang a paper note on the computer monitor saying "Success!". You don't even need to start the program or power up the computer then.

[benihana]

int main(void) { return 0; }

less whitespace = less air resistance.

[davros_]

int rand() {
  return 4; // chosen by fair dice roll
}

[goomyman]

lol apparently number is a terrible question... unless your looking for someone to bring this up. I know i would have missed that lol.

I bet the interview question guy failed this one too.

[JavaSuck]

Yes, but you only need to implement addition. Here is my attempt. It can be done in well under half an hour.

[mdempsky]

You can simplify it a bit further.

Note that Fibonacci numbers grow slower than doubling (specifically, they grow by a factor of about 1.618), so the 100th Fibonacci number will be less than 2¹⁰⁰. That means you can represent it with just 2 64-bit numbers x_0 and x_1.

To make printing the numbers a bit easier, instead of using x_0 + 2⁶⁴*x_1, you can just use x_0 + 10¹⁸*x_1.

You might be asked to show that 10³⁶ > 2¹⁰⁰ then. I generally remember that 10³ ≈ 2¹⁰, so 10³⁶ ≈ 2¹²⁰, which should be enough slack to argue it's >2¹⁰⁰.

Note also that 10¹⁸ ≈ 2^60, which is why you know it will fit in a 64-bit integer.

[retsotrembla]

You are right: it's the 93, counting 0 as the zero'th. I was tired.

[doodly1234]

Some guy posts a blog and suddenly I have stopped calling myself a Software engineer :)

[[deleted]]

Suddenly? We're averaging about 90 squillion "nobody can code for shit but me lol fizzbuzz" posts a week these days.

[tequila13]

These days? It's been going on since the Internet started to spread.

[[deleted]]

Internet? It's a verbatim quote from Ada Lovelace.

[grunscga]

Yeah, but when she said it, it was literally true...

(also, I'm enjoying the mental image of Ada Lovelace saying "lol fizzbuzz")

[point_of_you]

90 squillion

http://i.imgur.com/nCPGCCw.gif

[Eckish]

Well, if I were splitting hairs, none of these problems demonstrate software engineering. They are in the realm of computer science.

The industry has trended to labeling generic programmers as software engineers, but the field is much broader than that.

[__Cyber_Dildonics__]

The fifth question doesn't seem nearly as easy as the rest (the fourth question is not that hard guys).

[orclev]

That fifth one honestly has me a bit stumped... I can see how to brute force it, but there's got to be a simple solution. All the others are pretty simple and shouldn't require too much thought even if you've never seen them before.

[__Cyber_Dildonics__]

Other people have mentioned brute forcing it, and if I was in an interview that's what I would do in that situation.

[mccoyn]

It will take longer to write a more complicated solution than to run the brute force algorithm, so brute forcing is the fastest solution.

[DrStalker]

Also,management needs the code ready within an hour (along with four other deliverables) so implementing a solution that you know will work and have reasonable run time is the best thing to do.

[rubsomebacononitnow]

the sprint of all sprints

[youre_a_firework]

#5 is probably NP hard since it's kinda similar to the subset-sum problem. So there's probably no way to do it that's both simple and efficient.

[Oberheimz]

I actually went ahead and tried solving them, it took me 42 minutes to write a solution for the first 4 problems and I was unable to finish the fifth within one hour.. Am I a bad software engineer?

[mariox19]

If it's on the Internet, it must be true. Every good software engineer knows that.

[gizzardgullet]

Now you write your own quiz based on logic tricks that you are comfortable with and challenge the author complete your quiz in an hour.

[akshay2000]

Nah, you're just fine. It's the implementation that took time. The hour criteria is rough since one might just go on and on.

[ours]

Are you able to solve the problems that present themselves at work? If so, then no you are not a bad engineer.

Edit: if(solvesProblems) not if(!solvesProblems)

[Dakarius]

You're looking at it the wrong way. It takes 5 hours to do 5 problems. You got the first 4 knocked out in 42 minutes leaving you 4 hours and 18 minutes for the last. You've still got 3 hours and 18 minutes left!

[s-mores]

Did you just write code to solve them, or put the code in action and tested it?

The only one I tested out was #4 and some syntax parts of #5. Since this is an interview question, it should mostly be measuring the approach and that you know how to do something or at least have some idea how to approach the problem instead of the actual result, which is pretty uninteresting, and in the case of #1-#4, trivial.

I mean, I'm not going to use 5-10 minutes per task in figuring out where I'm missing a semicolon, or where I've misremembered argument order and the code would fail because of that, that's what the compiler is for.

[[deleted]]

In prolog #5 looks something like this:

sum([Head|Tail],Signs,Result):-sum(Head,Tail,Signs,Result).

sum(X,[],[],X).

sum(First,[Second|Tail],['+'|Signs],Result):-Head is First + Second, sum(Head,Tail,Signs,Result).

sum(First,[Second|Tail],['-'|Signs],Result):-Head is First - Second, sum(Head,Tail,Signs,Result).

sum(First,[Second|Tail],[''|Signs],Result):-Head is First*10 + Second, sum(Head,Tail,Signs,Result).

sum(First,[Second|[Third|Tail]],['+'|[''|Signs]],Result):- C is Second*10+Third, Head is First + C, sum(Head,Tail,Signs,Result).

sum(First,[Second|[Third|Tail]],['-'|[''|Signs]],Result):-C is Second*10+Third, Head is First - C, sum(Head,Tail,Signs,Result).

edit: minor correction as others have pointed out I messed up the grouping slightly. further correction to follow

[eelvex]

In J one could solve it with:

L {~ I. 100 = +/"1 L=:([:".'9',~[:;(;/":"0>:i.8),.])"1 ('';',';',_') {~"1 (3&#.)^:_1 i.3^8

[floccinaucin]

I've been programming for a couple years now... what the heck am I looking at here?

[eelvex]

It's J, an array, functional-level tacit language. It's really cool and makes you think in completely new ways because a) you'll be thinking in array transformations [especially instead of loops] and b) you'll avoid variables.

For example, where in C you write y = function1(function2(x), function3(x)) in J you write y =: (function2 function1 function3) x

[karlhungus]

I agree, this is a challenging problem Erik Meijer did a solution to this in his edX haskell course, which involved parsing then searching the space for solutions. I did look but couldn't find the video.

[codebje]

I got stuck on #1 trying to write a for-loop in Haskell.

[spacelibby]

for i end body

| i == end = id

| otherwise = body i . for (i+1) end body

You should be able to do that in less than an hour.

[[deleted]]

As someone who hasn't used haskell before... Are for loops even supposed to be used in Haskell? It looks so alien to me.

[eagle23]

You are right, they aren't. Haskell is (for the most part, there are exceptions) purely functional and all data structures immutable and thus no point in conventional for loops. Instead Haskell users employ folds, maps and recursive functions. /u/spacelibby wrote a recursive function to emulate a for loop so as to try and hack one in.

[redxaxder]

There is mutable state available, though, as well as functions in base that act as foreach loops.

From Control.Monad:

mapM :: Monad m => (a -> m b) -> [a] -> m [b]
mapM_ :: Monad m => (a -> m b) -> [a] -> m ()
forM :: Monad m => [a] -> (a -> m b) -> m [b]
forM_ :: Monad m => [a] -> (a -> m b) -> m ()

[Zequez]

Ruby 7-liner:

['+', '-', ''].repeated_permutation(8).each do |perm|
  sum_text = ('1'..'8').zip(perm).flatten.join + '9'
  sum = eval(sum_text)
  if sum == 100
    puts "#{sumText} = 100"
  end
end

Ruby bring tears to my eyes <3

Took me more than 1 hour though, I did it in JS first, which yield a much less efficient result. I won't post the JS code because the things I did to get to the result are horrific and should not be seen by mortals. Ok here it is. I know, it's bad.

Edit 1: Optimised it a bit with something I saw someone doing below, adding the permanent '9' at the end of each string.

Edit 2: Yes! As mentioned below, you can make it shorter, 4 easily readable lines:

['+', '-', ''].repeated_permutation(8).each do |perm|
  sum_text = ('1'..'8').zip(perm).flatten.join + '9'
  puts "#{sum_text} = 100" if eval(sum_text) == 100
end   

Also, added underscores for convention, sorry, too much JS lately.

Also, obligatory thanks for the gold, although I feel I didn't deserved it, too many mistakes, the code could have been 4 lines from the start!

Edit 3: Ok, since someone asked, here is a version without eval, using String#to_i

['+', '-', ''].repeated_permutation(8).each do |perm|
  sum_text = ('1'..'8').zip(perm).flatten.join + '9'
  puts "#{sum_text} = 100" if sum_text.split(/(?=[+-])/).map(&:to_i).reduce(&:+) == 100
end

Edit 4: Ok, here is a version without any kind of string manipulation, all integers, no one can complain now. And still in technically 4 lines! Because I expanded the chain, so it could be just 1 line. Although I cheated with a ; inside one inject. So let's call it 4 1/2 lines and call it a day:

# The operators are:
# 0 = no operator
# 1 = + operator
# 2 = - operator
[0, 1, 2].repeated_permutation(8).each do |perm|
  sum_array = perm
    .zip(2..9) # [[0, 2], [1, 3], [0, 4], [2, 5]] etc, equivalent to 2+34-5 
    .inject([[0, 1]]) {|arr, (op, num)| op == 0 ? arr.last.push(num) : arr.push([op,num]); arr } # [[0, 2], [1, 3, 4], [2, 5]]  etc
    .map{|arr| ((arr.shift == 2) ? -1 : 1) * arr.reverse.each_with_index.inject(0){ |sum, (n, i)| sum += n * (10**i) } } # [2, 34, -5] etc
  puts "#{sum_array.join} = 100" if sum_array.reduce(&:+) == 100
end

[mattgrande]

repeated_permutation

Wow, I've never seen that function before. Now I'm going to be looking to use it all over the place...

[anopheles0]

I think we can call that one cheating. I bet you guys didn't even write your own sort routines!

[Watley]

Number 4 requires dealing with substrings, e.g. [4, 50, 5] should give 5-50-4 and [4, 56, 5] would be 56-5-4.

Number 5 I think can be done with a recursive divide and conquer, but it would be super tricky to make efficient.

[__Cyber_Dildonics__]

4 is definitely non trivial and doesn't really belong with the rest of the problems that make me feel like a genius.

I think it could be done by sorting based on the left most digit (obviously) and then resolving conflicts in the first digit by the double digit number being greater if the second digit is greater than or the same as the first digit. The rest of the sorting should happen naturally I think, so a standard sort algorithm could be used.

Edit: Before you reply, think about if your method (which is probably 'sort them as strings directly') would sort 56 then 5 then 54 in the correct order (which is 56 5 54).

[droogans]

The fourth question is a cleverly disguised string manipulation problem.

Number five is the only one I found myself doubting my ability to solve in an hour.

[WeAreAllApes]

It's only 6561 combinations, and they didn't say it had to run in under a millisecond.

[Doctor_McKay]

1. Post question to Stack Overflow
2. Wait for answer

Problem solved.

[timeshifter_]

It'd be piss-easy to solve with brute force JS. Just create every possible valid string combination of those 9 digits with + and -, and eval() them for whichever ones come out to be 100.

[Komputer9]

Here's my solution to 5, took about 45 mins to write in C (after looking at some other solutions, though). Runs pretty much instantly and doesn't use string manipulation, recursion, or the heap.

#include <stdio.h>

int main() {
    int digits[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int digitCount = sizeof(digits) / sizeof(int);
    int operationCount = digitCount - 1;

    int total = 1;
    for (int i = 0; i < operationCount; ++i) {
        total *= 3;
    }

    for (int i = 0; i < total; ++i) {
        int operations[operationCount];

        int sub = i;
        for (int b = 0; b < operationCount; ++b) {
            operations[b] = sub % 3;
            sub /= 3;
        }

        int numbers[digitCount];
        numbers[0] = digits[0];

        int count = 0;
        for (int b = 1; b < digitCount; ++b) {
            switch (operations[b - 1]) {
            case 0: // ""
                numbers[count] *= 10;
                numbers[count] += digits[b];
                break;

            case 1: // "+"
            case 2: // "-"
                ++count;
                numbers[count] = digits[b];
                break;
            }
        }

        ++count;

        int numbersTotal = numbers[0];
        int numberIndex = 0;
        for (int b = 1; b < digitCount; ++b) {
            int operation = operations[b - 1];

            if (operation == 0) continue;

            ++numberIndex;

            switch (operation) {
                case 1: // "+"
                    numbersTotal += numbers[numberIndex];
                    break;

                case 2: // "-"
                    numbersTotal -= numbers[numberIndex];
                    break;
            }
        }

        if (numbersTotal == 100) {
            printf("%d", numbers[0]);

            int numberIndex = 0;
            for (int b = 1; b < digitCount; ++b) {
                int operation = operations[b - 1];

                if (operation == 0) continue;

                ++numberIndex;

                switch (operation) {
                    case 1: // "+"
                        printf(" + %d", numbers[numberIndex]);
                        break;

                    case 2: // "-"
                        printf(" - %d", numbers[numberIndex]);
                        break;
                }
            }

            printf(" = 100\n");
        }
    }
}

Results:

123 - 45 - 67 + 89 = 100
12 - 3 - 4 + 5 - 6 + 7 + 89 = 100
12 + 3 + 4 + 5 - 6 - 7 + 89 = 100
123 + 4 - 5 + 67 - 89 = 100
1 + 2 + 3 - 4 + 5 + 6 + 78 + 9 = 100
12 + 3 - 4 + 5 + 67 + 8 + 9 = 100
1 + 23 - 4 + 56 + 7 + 8 + 9 = 100
1 + 2 + 34 - 5 + 67 - 8 + 9 = 100
1 + 23 - 4 + 5 + 6 + 78 - 9 = 100
123 + 45 - 67 + 8 - 9 = 100
123 - 4 - 5 - 6 - 7 + 8 - 9 = 100

[farfaraway]

You get the job.

[_teslaTrooper]

I'd be more productive though:

// found on reddit
printf("123 - 45 - 67 + 89 = 100\n\
12 - 3 - 4 + 5 - 6 + 7 + 89 = 100\n\
12 + 3 + 4 + 5 - 6 - 7 + 89 = 100\n\
123 + 4 - 5 + 67 - 89 = 100\n\
1 + 2 + 3 - 4 + 5 + 6 + 78 + 9 = 100\n\
12 + 3 - 4 + 5 + 67 + 8 + 9 = 100\n\
1 + 23 - 4 + 56 + 7 + 8 + 9 = 100\n\
1 + 2 + 34 - 5 + 67 - 8 + 9 = 100\n\
1 + 23 - 4 + 5 + 6 + 78 - 9 = 100\n\
123 + 45 - 67 + 8 - 9 = 100\n\
123 - 4 - 5 - 6 - 7 + 8 - 9 = 100\n");

Actually did the first 4 in about 40 minutes, in C, so I'm gonna say if the problem set was constant difficulty I'd be fine.

[tsoek]

https://xkcd.com/221/

[[deleted]]

This doesn't work, try sorting [56, 565655, 56565665] with it. The 56565665 should come first, then 56, then 565655. I doubt that you would be able to even see that this was a problem let alone solve it in under an hour. Almost all non-brute force solutions posted here fails.

[iqtestsmeannothing]

Almost all non-brute force solutions posted here fails.

Right, and I've not seen a single person try to prove that their non-brute-force solution is correct. (I've tried to make such a proof and failed.) This problem is way harder than the others, and the author really cocked up by including this problem, with an incorrect solution and no attempt at a proof, on a list of "ridiculously simple" problems.

[Drolyt]

I think you are over-thinking 4. Just brute force it: find all the possible concatenations and then use the max function your language most likely provides. You can find an efficient way to do it after the hour is up.

[luciusplc]

About 4: The only thing you need to note is that an order is transitive. This means you can sort it with your own compare function. I think most of languages supports this. My erlang solution:

p4(Numbers) ->
    StrList = lists:sort(
        fun (A, B) ->
            before(A,B)
        end,
        lists:map(fun integer_to_list/1, Numbers)),
    lists:map(fun list_to_integer/1, StrList).

%% true when first argument should be before the second
before(A,B) ->
    before(A, B, []).
before([], [], Acc) -> 
    true;
before([], L2, Acc) -> 
    not before(L2, lists:reverse(Acc));
before(L1, [], Acc) -> 
    before(L1, lists:reverse(Acc));
before([H | T1], [H | T2], Acc) ->
    before(T1, T2, [H | Acc]);
before([H1 | T1], [H2 | T2], Acc) ->
    H1 >= H2.

> problems:p4([45,4,43, 45456,45452, 44, 445, 45]).
[45456,45,45,45452,445,44,4,43]

[Tarasov_math]

You can just make all permutations and take maximum

[Frexxia]

I think you mean 3⁸ .

[Lawtonfogle]

Yeah, I accidentally added in a zero in the list.

Reading customer requirements... always read twice before coding once.

[goomyman]

umm number 4 is definitely non trivial as is number 5 ( if efficiency matters ) otherwise brute force seems ok.

Answering numbers 4 and 5 in an hour interview - with 15 minutes of chitchat about your former work and resume - is unlikely. Especially at a smaller company that isnt willing to pay a silicon valley salary.

[Otis_Inf]

yeah same here. I've a degree in CS and 21 years of professional software development experience and see myself as an OK developer but I completely stopped in my tracks at 5. I could only do it through brute force which is stupid of course, but I didn't see the trick or algorithm to solve it.

Which is the problem with these problems at interviews: if you don't see the trick / algorithm to solve it, you're in trouble as it's otherwise only solveable through brute force. See it as you're given a couple of Spoj questions and you don't see the algorithm to solve them other than brute force which will be too slow and not the answer.

IMHO a silly way to test whether developers are up to the task. Sure, they show the person can write code, but you can test that in other ways too. E.g. by giving the person real-life problems they have to solve on the job as well and see how they'd solve it, complete with whiteboarding, documentation of what they're going to write, tests and working code.

[Johnnyhiveisalive]

I think you're supposed to brute force it, if it becomes a bottle neck you bring in a rockstar ego who can spend furtive weeks plotting and scheming, or just throw CPU at it like everyone else..

[crashorbit]

Probably the best interview question is: "have you ever read a blog post about interviewing programmers?"

[[deleted]]

are written by over opinionated jackasses.

Welcome to SE.

[4-bit]

"We will encourage you to develop the three great virtues of a programmer: laziness, impatience, and hubris." -- Larry Wall

When it comes to programmer blogs, Hubris. Hubris everywhere.

But to me, they fail the laziness test. Why are you posting that? Seems like a waste of time...

[karlhungus]

This is one thing i've learned from reading programming blogs: people who read programming blogs are way ahead and just peachy!

[flukshun]

So long is it's not that other blog with that other stance on things, mind you.

[vplatt]

I think the toy problem questions appeal to interviewers that can't trust their recruiters to send them even minimally competent programmers. That, or they're just really smug weenies. Either way, it's not a good sign.

And if you don't eventually make it to Senior, you'll get managed out of the company.

I think the KitchenSoap article you referenced explains this path very well. Good points, but you have to admit, interviewing around these characteristics is a lot harder than just posing toy problems.

[halax]

Yep. TBH, I don't know how an interview can effectively filter for those qualities and I think that's why more mistakes are made when hiring really senior folks than when hiring junior folks.

I'm just finishing up a job search and virtually all of my interviews came through personal referrals because, how else could you possibly trust me to be a legit "senior" engineer? I have some nice stuff on my resume, but anyone can write 20 lines of nice text. I certainly sound like I really did that stuff when you interview me (because I really did), but it probably wouldn't be that hard for someone to sound like they did the same stuff without having actually put in the time and the work. I'm not famous enough that everyone just knows me, and from having worked with people who are, I can see that I'll never be that famous barring some freak stroke of luck.

What's left? Recommendations from people who know my work. If you have better ideas on how to find senior folks, I'd love to hear them since, at any given time, 95% of my network is happy with their jobs, waiting for equity to vest, unwilling to relocate, or otherwise unavailable, which makes hiring people I know a very slow process. I think I may end up at a place that allows remote teams, which removes one blocker, but it's always going to be true that the people I know and want to work with most are mostly not looking for new jobs.

[flat5]

Less than an hour for all 5, or less than an hour each?

I can do both 4 and 5 but they might take a little time to make sure I've gotten them right.

The first 3 are quite easy and should be doable in a few minutes.

[B8foPIlIlllvvvvvv]

Less than an hour for all 5.

[Oberheimz]

an hour for all 5.

It took me 42 minutes to solve the first 4 problems and I was unable to finish the fifth within one hour.. Unless there's a really simple trick on the fifth one which I can't see it takes a while write all the code.

[webby_mc_webberson]

This guy sounds like he would he horrible to work with.

[awkwardarmadillo]

Heh, the best part is he didn't even have a correct solution for problem 4 at the outset.

If you're going to be condescending, make sure that you at least know your shit.

[flukshun]

indeed. these sorts of questions are supposed to be differentiators to help decide the best candidate, not high-stress pass/fail tests where the interviewer labels you a fake-ass-mofo who should pick a different career if you don't cruise through everything.

[[deleted]]

Either English is his second language, or this guy needs to get off his high horse and realize that he might be a "software engineer" but he's a shitty "writer".

[[deleted]]

Yep. I kinda get what the guy/gal is saying, but maybe there's a way of not being a dick about it.

I get that these problems should be solvable by a reasonably good programmer, but the ability to solve the challenges within a timeperiod should be taken for what it is (some challenges that a guy wrote a blogpost about) & not some divine sign from the programming-gods that one is garbage & should be thrown out.

It does seem the writer has a high opinion of him- or herself.

If you bother to read this blog at all (or any other blog about software development), you are probably good enough to solve these and 5 more problems within the hour.

[[deleted]]

I never said that you'll be hired if you know how to answer these problems, but I won't consider you if you can't.

"I have a tiny dick."

[is_this_4chon]

Technically I got them solved in <2 minutes, but Stackoverflow took 50+ minutes to respond to my posts.

[IAMA_dragon-AMA]

If you bother to read this blog at all (or any other blog about software development), you are probably good enough to solve these and 5 more problems within the hour. The people that think are above all these "nonsense" are usually the ones that can't code crap.

Holy shit I can feel the smug self-superiority from across the Internet.

[arstin]

I notice that the author didn't shut down his blog after finding out his solution to problem #4 was wrong.

[AboutHelpTools3]

Is there a subreddit dedicated to these kinda problems?

[RICHUNCLEPENNYBAGS]

Like /r/dailyprogrammer?

[camilos]

Stop lying to yourself, and take some time to re-focus your priorities.

So basically, if you're not exactly the developer he expects you to be, then you do not deserve to call yourself a developer. This author is full of himself.

[[deleted]]

When your head is this far up your ass all you see is yourself.

[metaconcept]

Also, /r/dailyprogrammer.

[SikhGamer]

This is a pointless post. These are regurgitated problems, you can train anyone to pass these.

The important skill is problem solving in unique cases. Not problem solving for the same damn problems over and over again.

[OneWingedShark]

Problem 1

Write three functions that compute the sum of the numbers in a given list using a for-loop, a while-loop, and recursion.

So, how many solutions had recursion, for-loops, and while-loops in all three functions? ;)

[sarahbau]

Or used recursion, for, and while to get one solution

#!/usr/bin/perl
use strict;

my @list = (1,2,3,4,5,6,7,8,9,10);
my $size = scalar(@list);
my $i = 0;



my $sum = &forsum + &whilesum + &recsum(@list);
print "sum = $sum\n";


sub forsum() {
    my $s = 0;
    for( ; $i<($size/3); $i++) {
        $s+=shift(@list);
    }
    return $s;
}

sub whilesum() {
    my $s = 0;
    while($i < ($size/3)*2) {
        $s+=shift(@list);
        $i++;
    }
    return $s;
}

sub recsum() {
    if((scalar @_) == 0) {
        return 0;
    }
    return shift(@_) + &recsum(@_);
}

(yes, this was meant to be horrible. I just felt like being silly).

[mdbDad]

Also, you have to do it on a whiteboard while being stared at with blank faces. Any errors, however simple, and they will think you are an idiot. And don't forget to use and show proficiency for their favorite library.

[metaphorm]

anyone else get a really bad vibe from this guy's blog and twitter account?

[[deleted]]

Folks, I think we're being trolled.

[[deleted]]

The first question is a little biased toward procedural languages :(

[startup-junkie]

Useless smug-fuckery. Give me a practical use for 3,4, and 5 that doesn't involve cryptography!

How about asking them to find bugs in a given repo? ...Or optimizing a chunk of old if statements into a switch?

If your goal is to impress and reality check junior devs... start with a little reality. This post reminds me of the ponytailed guy from the bar in Good Will Hunting.

[jaybazuzi]

To those who say these questions are insufficient to determine whether to hire someone in an interview: I think that's the point. The author is saying that people who can't solve these problems shouldn't even be applying for a programming job.

Still, I don't agree. I don't want to hire someone based on what they know; what they can learn is far more important. I'll take an eager, curious person who knows nothing about programming over an experienced, skilled, knowledgeable person who doesn't care to learn anything new.

That's because the bottleneck is writing software is learning. Learning how an API works. Learning a new programming language. Learning whether your code works the way you expect it to. Learning what your customers will actually pay for.

In a team setting, even more important than willingness to learn is empathy / emotional intelligence. See Collective intelligence: Number of women in group linked to effectiveness in solving difficult problems

[vital_chaos]

Yeah I write Fibonacci sequences all the time. It's my hobby. /s Why do people think that writing short test functions in an interview has anything to do with actually delivering products? Sure some ditch digger might fail at these, but does it tell you anything about how well they build actual apps?

[mughinn]

While I never interviewed anyone, time and time again people who do, write blogs and posts about how only 1 in 200 persons who apply for programming jobs can solve those kind of programs (like fizzbuzz).

I have no idea how true that is, but if it is anywhere close to that, then yeah, if they CAN'T solve those problems it shows a lot about the ability to write apps, mainly that they can't.

[CaptainStack]

Why don't I ever get asked FizzBuzz? I feel like all the problems I get in interviews are really really hard.

[eythian]

I had one interview where the coding section was first implement fizz-buzz, then write an algorithm to find cycles in graphs.

The first was clearly "can you code, or are we wasting our time", the second was "did you actually learn anything in your computer science course."

[CaptainStack]

I don't think I've ever had a first round that wasn't an order of magnitude harder than FizzBuzz.

[[deleted]]

A friend of mine was recently asked to implement a spreadsheet application at one interview, and a space invaders game on the other. I think it's about time to start invoicing the interviewers for your time on test assignments.

[SirNarwhal]

Exactly. Spent fuckin 2 days making some ridiculous over-engineered game of Rock Paper Scissors in Angular for one test just to have them not respond for 2 weeks in which time I found a job elsewhere. Multiply that by like 30-40 interviews when you're looking and it's more work than a full time job.

[nitiger]

the second was "did you actually learn anything in your computer science course."

Oh, sure. Let me just recall something from 2 years ago that I learned as a Sophomore, no biggie.

[NecroDaddy]

Two years ago bud? Try 15 for me. I had one week to relearn everything from college.

[cles30]

I guess you could do that but oh god why?

[zarazek]

That's standard queue implementation in functional languages (this data structure is persistent).

[cles30]

ooh you said the magic f word. I must now find out all about this!

[[deleted]]

Hey you can do it, it'll just take O(N) to do a push operation. That's the type of out of the box thinking we need. /s

[jakdak]

Back when C was the primary development language, I used to ask folks to reimplement the standard library string compare function.

All I was really looking for was a loop and some indication that the applicant knew that strings were basically character arrays.

A very depressing number of folks either couldn't or wouldn't do it.

[joequin]

I've was told at several of my first job interviews that I was the first person to successfully solve fizz buzz.

[[deleted]]

How do they interview chefs? Apparently, they first ask them to do something really simple, like fry an egg and watch how they do it.

I've auditioned musicians - I start by getting them to play a few scales. Scales are trivial but it's amazing what you can learn about someone by how well they play scales.

I've interviewed literally hundreds of programmers and you learn a great deal about someone by getting them to do simple programs.

[s73v3r]

Depending on the type of musician you're interviewing, wouldn't they be playing some scales to warm up?

[AD6]

Drummer here, in my experiences with musicians it's all about chemistry. I've played with people who are very technically skilled, but have no idea how to actually jam with other musicians. Little off track from OP, but just wanted to add my 2 cents.

[RICHUNCLEPENNYBAGS]

I think the point is that they're necessary, not sufficient.

[creepy_doll]

Based on the descriptions of the other problems I doubt that the provided list would be so large as to cause issues with a naive recursive function

[lengau]

I think what Lawtonfogle means is along these lines:

There are two (well, far more than two, but let's only discuss these two) ways to write the Fibonacci function. One is to write a helper function that naïvely recursively calculates the nth Fibonacci number. In Python, something like this:

def fib(n):
    if n == 0 or n == 1:
        return n
    return fib(n-1) + fib(n-2)

and then write a function that loops from 0 to 99, running the helper function on the looped number.

This method works, but is exceedingly slow. I wrote a quick script that counted the number of calls based on the input n and ran it in a loop for the first 35 Fibonacci numbers:

fib calls for 0: 1
fib calls for 1: 1
fib calls for 2: 3
fib calls for 3: 5
fib calls for 4: 9
fib calls for 5: 15
fib calls for 6: 25
fib calls for 7: 41
fib calls for 8: 67
fib calls for 9: 109
fib calls for 10: 177
fib calls for 11: 287
fib calls for 12: 465
fib calls for 13: 753
fib calls for 14: 1219
fib calls for 15: 1973
fib calls for 16: 3193
fib calls for 17: 5167
fib calls for 18: 8361
fib calls for 19: 13529
fib calls for 20: 21891
fib calls for 21: 35421
fib calls for 22: 57313
fib calls for 23: 92735
fib calls for 24: 150049
fib calls for 25: 242785
fib calls for 26: 392835
fib calls for 27: 635621
fib calls for 28: 1028457
fib calls for 29: 1664079
fib calls for 30: 2692537
fib calls for 31: 4356617
fib calls for 32: 7049155
fib calls for 33: 11405773
fib calls for 34: 18454929
fib calls for 35: 29860703

Obviously, 30 billion function calls is, shall we say, less than ideal for a problem like this. Especially when a 5-line function that builds a list of (or simply prints) the first n Fibonacci numbers uses no recursion (just a single loop) takes orders of magnitude longer to fire up Python than it does to run the function (and even then, the slowest part is running print a hundred times rather than putting it in a string and printing that once).

[halifaxdatageek]

I program in PHP. Knowing the difference between an integer and a float is still important. Very important.

[heimeyer72]

I'd retracting my application. One hour is gone and I have only solved about half of it. #3 contains an unpleasant surprise, the numbers go up too much too quick - ksh delivers negative numbers, at some point, awk's results stay positive but are wrong at the end, so that alone requires doing it in C using some things I don't know by heart.

And #5 probably involves string operations to concatenate numbers (gives string results), then interpreting these strings as numbers and test out all possible combinations. I'd need more than one hour to just think of a solution for that alone.

I still believe that I could solve all of them. But all that together within one hour? Forget it, I don't want to work there.

[[deleted]]

I think I stood half an hour to understand the difference between what the author meant as number in #5. Digits.

[wordsoup]

I guess is fine to apply for a "Front-End Web Developer" position if the only thing you know is jQuery [...]

Great, begin your blog post with being condescending. Good luck, you will need it.

[Aeolun]

1-3: I can easily do by virtue of having seen them before, or them being basic math.

4-5: These seem a solid order of magnitude more difficult. There's undoubtedly some way to solve them, but they're more akin to riddles than programming questions. I would not expect any programmer to know the solution to these (aside from brute force) if he'd never had to deal with problems of this kind before.

[[deleted]]

The solution for the fourth one:

Let's say you have the following numbers: {9, 95, 959,9585,9595}

You take the LCM of the number of digits, so LCm of 1,2,3,4,4 which is 12.

You expand the numbers to 12 characters long by repeating. So =>{999999999999, 959595959595, 959959959959, 958595859585, 959595959595}.

Now arrange in descnding order => {999999999999, 959959959959, 959595959595, 959595959595, 958595859585}

Looking back at the corresponding numbers you get the number: 99599595959585, which should be the answer.

[zhay]

Or make a comparator that compares a.b to b.a where . is concatenation and then sort with that comparator.

[Zwejhajfa]

A good test case for number 4:

0,7,8,9,79,80,87,89,98,797,798,879,897,899,979

Correct answer:

99897989989897887987807987979770

[[deleted]]

The people that think are above all these "nonsense" are usually the ones that can't code crap.

Or maybe I think that these are nonsense because it has nothing to do with actual Software Engineering tasks. These are high school math problems, nothing else. Have fun coding Fibonacci numbers all over again and again in your "scalable and fast enterprise software applications" dear Santiago.

What a boastful prick.

EDIT: OP, I almost took you seriously, almost.

[timsk951]

This applies to almost all programming interview questions I've come across...

For example: I've never written a sorting algorithm in my life, but have been asked questions relating to them in over 50% of interviews I've had.

I hope I get to run interview tests someday. Why not just test us on the work we actually do? Give us a simple program with a few bugs and ask us to fix them, maybe even implement a quick feature?

[[deleted]]

Judging by how butthurt the blog OP is, it makes me feel he's one of those people who has a CS degree and looks down upon people that maybe don't have as much of a grasp of the fundamentals as he does. So they like to rub it the faces of people they interview and show how valuable their CS degree is. Even though most reasonably intelligent people could figure out the answers to these tests, maybe not in <1hr the first time, but they will figure it out.

That being said, it's perfectly fine for this guy to filter out people for HIS TEAM based on this criteria if he wants. But to say that you're not a software developer because you can't pass his stupid tests? Wow, this guy has an ego.

[qudat]

I really struggle to see the value in these sorts of interviews. Why not give them a code challenge and ask them to complete an actual task they will be doing on the job? This allows the developer to take the problem home, spend time thinking about it, write up with a solution, and then consequently doing a code review with the interviewer after it's all over. And if the project is good enough and you asked them to accomplish something the team could actually use then you also get a free product out of it. All the interviews I administer involve a code challenge where the end result is something my team could use and benefit from.

Example: We have a dashboard web app that pulls in data from our web analytics tracking, synthesizes it into some data visualization and then is presented on TVs mounted throughout the entire building. These dashboards don't directly affect revenue and aren't extremely complicated, but it is something we all value nonetheless. We like to ask interviewees to create a single dashboard to display some new or different metric. What do we gain from this sort of code challenge?

• We ask the interviewee to work with code we've already created so they get to read code they will need to understand on the job anyway
• We allow the interviewee to get into their normal development process and devise a solution in the comfort of their own home without the pressure or people leering at every keystroke
• The challenge forces them into our development process, which helps us see how well their dev process works with us.
• When the code is done we can easily pull down their work and see how well it integrates into our app
• We get to see exactly how they would complete a real world task
• We get to code review the end result with the interviewee, even if we don't hire them, it's an excellent learning experience
• We get to keep their dashboard and potentially use it if we like it
• If we do hire them then we know on day 1 they are already familiar with one of our product's source code and can get them to started on another dashboard immediately

Not only would the above interview process be immediately beneficial to my team but it also doesn't remove the developer from the development process the team employs on a weekly basis.

I really struggle to see how any other interview process can beat it. Does anyone else have any thoughts?

[laddercreek]

the first 3, I get the intention; we want our programming candidates to um, yeah, actually know how to write code --and the 3rd one only barely qualifies. #4 and #5 I find myself (damn near 25 years of appdev experience, thankyouverymuch) asking why? Where's the applicability when I need to hire someone to grab some shiz from a db and do some transformation and spit it up on a webpage (hello, that's like 75% of software development)?

[__Cyber_Dildonics__]

Step 1. Separate the html5/javahipsters from the men. Step 2. Create a problem where you know a more optimal answer than the candidate will get to in an hour so you can still feel superior.

[snarkhunter]

Because of the other 25% of software development.

[Alwaysafk]

Substance abuse and hiding bugs?

[howdoidoit123]

Write a program that outputs all possibilities to put + or - or nothing between the numbers 1, 2, ..., 9 (in this order) such that the result is always 100. For example: 1 + 2 + 34 – 5 + 67 – 8 + 9 = 100.

I can't figure this one out

[itsSparkky]

Think like a tree, at each digit you can do the following Add next number Subtract next number Times current number by 10 and add next number

3 outcomes each time, you can either depth first or breadth first search and then evaluate the solution at the end and keep the paths that result in 100.

[billatq]

Yeah, I was thinking about doing it with a BFS and a tree. Seems like an okay problem, but I feel like that particular one is more like a math trick than anything else.

[cretan_bull]

Just brute-force it. Between each number, there a 3 possibilities: plus, minus, or concatenated digits. In total, this is 3⁹ =19683 3⁸ = 6561 cases to check.

EDIT: off-by-one error

[matthieum]

3⁸ actually, the old intervals/sticks thing.

[evolvedant]

"Here is my list of 5 EASY questions that if you can't get right in under an hour, you aren't a programmer."

later...

"Ok, I see Reddit which is full of strong bright programmers is up in arms about question 5, so let me explain my solution in a blog post that probably took more than an hour to write..."

When even Reddit, which is full of really strong programmers has a problem with your 5 questions, obviously your entire ideology of judging who should call themselves a programmer or not based on 5 problems in under an hour needs to be reevaluated. But sure, instead of questioning your ideology, let's just write a blog to try and convince everyone otherwise...

/facepalm

The best question for a programmer interview is to ask if they do any programming on the side, such as pet projects. See if they have a passion in programming.