6 ms·

Where Are All the Qualified Programmers?

14 points by nickb 19y ago

downer 19y ago
> like "How do your reverse an array without a temporary variable?" You hard-code it using XOR. Note you can't even do a for-loop, as that's using an extra variable. Of course hand-unrolling a loop takes extra memory because it's so many extra lines so there's no point. a ^= b b ^= a a ^= b This is very unlikely to be something that occurs to programmers who haven't had to XOR recently; if you aren't writing your own hash or crypto or codec functions then you probably haven't used it in a while. Now that you've seen this, you'll remember it and so if anyone asks, you won't be figuring it out again, just recalling. IMO it's a pretty useless way to weed people out, kind of like testing people on chess by random arrangements of pieces. Chess experts remember actual legal positions that occur in games much better than non-players, but they are no better at remembering positions that never occur -- a bunch of kings on a chessboard, some in adjacent squares, for example. Likewise, this kind of pattern NEVER occurs in what most people program; it's just implausible.
- neilc 19y ago
  You can use a for loop, if you step through the array with pointer arithmetic. On the assumption that you're given the array length (or else that the array is of fixed size), you don't need to hand-unroll the loop, which wouldn't handle a variably-sized array anyway. But I agree that it's a bad interview question.
  - downer 19y ago
    Doing p++, len-- uses two temporary variables.
    - neilc 19y ago
      You don't need a temporary variable for "p" -- if the task is to write a function, you must have a pointer with the address of the start of the array, not an array variable as such. And yeah, you need some way to tell the length.
      - downer 19y ago
        ...and where you are in the array, hence the temp variable. Write it out to see. So it still doesn't work, even if you use a function to "cheat" and get a "free" pointer (which, by the way, wasn't what the task said).
        neilc 19y ago
        Yeah, I suppose you'd need 1 temporary variable. Your solution doesn't work either, though: doing the freshman XOR trick some arbitrary fixed number of times just reduces to the XOR trick, which is plainly not what the task asked.
        downer 19y ago
        It does work, you do the 3-step XOR with a[0] and a[last], then a[1] and a[last-1], etc. The 3-step XOR from the OP swaps the data. Here it is with a 4-element array, a[0] through a[3]: a=[100,200,300,400] a[0] ^= a[3] a[3] ^= a[0] a[0] ^= a[3] a[1] ^= a[2] a[2] ^= a[1] a[1] ^= a[2] a [400, 300, 200, 100] (Pretend this list is an array, it's just for illustrative purposes)
        neilc 19y ago
        Well, obviously the XOR swap works. But how do you use that to reverse an array of variable size? (i.e. where "last" isn't known at compile-time, so the number of swaps isn't known in advance).
        downer 19y ago
        You don't; it's basically, "here's an array, now reverse it" (keep in mind a pointer is not an array). http://www.lysator.liu.se/faq/c-faq/c-2.html http://www.lysator.liu.se/faq/c-faq/c-2.html The general point is that interviews of this type are counterproductive.
        neilc 19y ago
dpapathanasiou 19y ago
The point about H1-Bs and lower salaries has some merit, but the author fails to mention perhaps the most significant reason. Good programmers don't want to work at dull jobs in large companies (though there are some exceptions, e.g. for i-banks, hedge funds, etc., since people will tolerate dull tasks for substantially better than average pay).
nradov 19y ago
I don't understand complaints about a shortage of developers. In a free market economy there is no such thing as a shortage, by definition. There may be occasional, temporary imbalances between supply and demand. But over several years the market will equalize at the natural clearing price. If there was really a shortage then labor prices would increase sharply, and that would cause more smart people to get educated and enter the market. Of course, when most industry executives complain about a programmer shortage what they really mean is they are having trouble finding smart, experienced people who will work long hours on boring projects for low pay. Imagine that.
- Tichy 19y ago
  That seems incorrect to me. Sure the market will find the right price for a programmer, but that doesn't mean the economy as a whole could not be better off with more programmers. As an example, imagine that Web Development was so difficult that only one programmer on earth could pull it off. Maybe that programmer would get paid millions or even billions, but there sure as hell would not be as many useful web applications around as there are today.
  - geebee 19y ago
    True - lots more talented people would benefit the world. But you have to consider opportunity cost as well. If web application development required genius level knowledge, then you'd have to convince one of the best minds in some other critical field to switch over to it. Suppose the only person who could write webapps is also capable of engineering a sustainable and pollution free source of energy. The world might be better off with no webapps at all. A lot of people have pointed this out - it actually takes quite a bit of talent to write reasonably unbuggy code that updates payroll from the eight different departmental database systems. It's just terribly boring, and not especially well paid, so the people with this kind of talent either do other things in the software world, or don't work in software at all.
    - Tichy 19y ago
      Sure, I was only taking issue with the claim "In a free market economy there is no such thing as a shortage, by definition". Let's take food as another example: if there is not enough food to feed all people it doesn't help much that the market will establish a fair price for the food. Some people are still going to starve. In the long run the market might try to provide more food, but perhaps there simply is a limit to the amount of food that can be provided. Likewise for good programmers - maybe the amount of people who are intelligent enough is severely limited? Although I suppose woith 6 billion people, there should be the one or other with sufficient brains...

14 points by nickb 19y ago

> like "How do your reverse an array without a temporary variable?" You hard-code it using XOR. Note you can't even do a for-loop, as that's using an extra variable. Of course hand-unrolling a loop takes extra memory because it's so many extra lines so there's no point. a ^= b b ^= a a ^= b This is very unlikely to be something that occurs to programmers who haven't had to XOR recently; if you aren't writing your own hash or crypto or codec functions then you probably haven't used it in a while. Now that you've seen this, you'll remember it and so if anyone asks, you won't be figuring it out again, just recalling. IMO it's a pretty useless way to weed people out, kind of like testing people on chess by random arrangements of pieces. Chess experts remember actual legal positions that occur in games much better than non-players, but they are no better at remembering positions that never occur -- a bunch of kings on a chessboard, some in adjacent squares, for example. Likewise, this kind of pattern NEVER occurs in what most people program; it's just implausible.

neilc 19y ago
You can use a for loop, if you step through the array with pointer arithmetic. On the assumption that you're given the array length (or else that the array is of fixed size), you don't need to hand-unroll the loop, which wouldn't handle a variably-sized array anyway. But I agree that it's a bad interview question.
- downer 19y ago
  Doing p++, len-- uses two temporary variables.
  - neilc 19y ago
    You don't need a temporary variable for "p" -- if the task is to write a function, you must have a pointer with the address of the start of the array, not an array variable as such. And yeah, you need some way to tell the length.
    - downer 19y ago
      ...and where you are in the array, hence the temp variable. Write it out to see. So it still doesn't work, even if you use a function to "cheat" and get a "free" pointer (which, by the way, wasn't what the task said).
      - neilc 19y ago
        Yeah, I suppose you'd need 1 temporary variable. Your solution doesn't work either, though: doing the freshman XOR trick some arbitrary fixed number of times just reduces to the XOR trick, which is plainly not what the task asked.
        downer 19y ago
        It does work, you do the 3-step XOR with a[0] and a[last], then a[1] and a[last-1], etc. The 3-step XOR from the OP swaps the data. Here it is with a 4-element array, a[0] through a[3]: a=[100,200,300,400] a[0] ^= a[3] a[3] ^= a[0] a[0] ^= a[3] a[1] ^= a[2] a[2] ^= a[1] a[1] ^= a[2] a [400, 300, 200, 100] (Pretend this list is an array, it's just for illustrative purposes)
        neilc 19y ago
        Well, obviously the XOR swap works. But how do you use that to reverse an array of variable size? (i.e. where "last" isn't known at compile-time, so the number of swaps isn't known in advance).
        downer 19y ago
        You don't; it's basically, "here's an array, now reverse it" (keep in mind a pointer is not an array). http://www.lysator.liu.se/faq/c-faq/c-2.html http://www.lysator.liu.se/faq/c-faq/c-2.html The general point is that interviews of this type are counterproductive.
        neilc 19y ago

dpapathanasiou 19y ago

The point about H1-Bs and lower salaries has some merit, but the author fails to mention perhaps the most significant reason. Good programmers don't want to work at dull jobs in large companies (though there are some exceptions, e.g. for i-banks, hedge funds, etc., since people will tolerate dull tasks for substantially better than average pay).

nradov 19y ago

I don't understand complaints about a shortage of developers. In a free market economy there is no such thing as a shortage, by definition. There may be occasional, temporary imbalances between supply and demand. But over several years the market will equalize at the natural clearing price. If there was really a shortage then labor prices would increase sharply, and that would cause more smart people to get educated and enter the market. Of course, when most industry executives complain about a programmer shortage what they really mean is they are having trouble finding smart, experienced people who will work long hours on boring projects for low pay. Imagine that.

Tichy 19y ago
That seems incorrect to me. Sure the market will find the right price for a programmer, but that doesn't mean the economy as a whole could not be better off with more programmers. As an example, imagine that Web Development was so difficult that only one programmer on earth could pull it off. Maybe that programmer would get paid millions or even billions, but there sure as hell would not be as many useful web applications around as there are today.
- geebee 19y ago
  True - lots more talented people would benefit the world. But you have to consider opportunity cost as well. If web application development required genius level knowledge, then you'd have to convince one of the best minds in some other critical field to switch over to it. Suppose the only person who could write webapps is also capable of engineering a sustainable and pollution free source of energy. The world might be better off with no webapps at all. A lot of people have pointed this out - it actually takes quite a bit of talent to write reasonably unbuggy code that updates payroll from the eight different departmental database systems. It's just terribly boring, and not especially well paid, so the people with this kind of talent either do other things in the software world, or don't work in software at all.
  - Tichy 19y ago
    Sure, I was only taking issue with the claim "In a free market economy there is no such thing as a shortage, by definition". Let's take food as another example: if there is not enough food to feed all people it doesn't help much that the market will establish a fair price for the food. Some people are still going to starve. In the long run the market might try to provide more food, but perhaps there simply is a limit to the amount of food that can be provided. Likewise for good programmers - maybe the amount of people who are intelligent enough is severely limited? Although I suppose woith 6 billion people, there should be the one or other with sufficient brains...