Why it took 2 days(48 hours) to transport a package from point A to point B by UPS Mail Innovations, which is only a 30 minutes drive, or a 6 hours walk?

Apparently, this next generation and innovative logistics service is either operated by elephants or snails.

UPS Mail Innovations - Next generation logistics operated by elephants or snails.

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I am going to have a face-to-face interview with a candidate of a PHP programmer position this afternoon. I was told to prepare some technical questions for the interview.

If a candidate earns an face-to-face interview opportunity, that means his resume should have a very good match to the position requirement. However, people can put anything on their resumes, there is no way to tell whether the information on the resume is true or not (and referencees guarantee will give you good feedback on the candidates). That’s why a face-to-face interview is really important.

I will have around 30 minutes to 1 hour to interview a candidate, how can I get the most information from him to help myself making this decision?

After googling on the web, I found tons of information about how to interviewing a programmer, but most of them are related to really technical questions, such as “How do you solve this math puzzle?”, or “What’s the meaning of double-dollar variable in PHP?” etc. I think these questions are not efficient and effective enough to judge the skill of the candidates. Personally, I don’t like these types of questions at all because I think it does not help to judge a realistic performance of a person. I prefer some more realistic questions.

So, I end up designing a test by myself. It is nothing more than a simple html form (e.g., a form to update users’ contact information). The candidate will be asked to implement the functions to update the records. I think this is pretty closed to what I do in my work, i.e., Create, View, Update and Delete record.

Well, this question sounds pretty simple, and I think there are plenty of hidden traps. Here are what I expect in the codes:

  • Core function, i.e., Updating the record – 40%
  • Validating the inputs(e.g., don’t store a negative number into age column, make sure the ID exists etc) – 10%
  • Performance (e.g., Update the record only if the records have been changed by the users.) – 10%
  • Handling simultaneous update (e.g., lock the record before update) – 10%
  • Security (e.g., storing the configuration out of the web server scope, prevent online attack etc) – 10%
  • Development time(e.g., spending 2 hours ends up with very few features is not acceptable) – 10%
  • Think outside the box(e.g., Suggesting to use Ruby on Rails to shorten the development time, using jQuery for client-side validations etc.) – 10%

I believe that if a person can do great in a simple task, he will do great in a complex task. Unfortunately, it is not easy to look for a good programmer.

Updates (August 31, 2009):

The answers I received from the candidates are pretty interesting and filled with tons of surprise. Some of the answers go beyond my imaginations. Here are few examples:

  • One candidate sent me a package with all of the source codes. Unfortunately, none of the codes works. Apparently, he forgot the golden rule of software development: A software must work.
  • Another candidate sent me a package with tons of files. After I read the codes, I found that the codes were copied from other projects with very minor modifications. This kind of candidates should be avoided because cleaning up the code is a basic responsibility of a programmer.
  • A candidate has spent a lot of efforts on defining the variables (More than 20 variables were defined in the configuration sections), but he only put one line of comment (and no code implementations) inside the validation function, i.e.,
    //Validation goes here...

    He would impress me if he included at least one validation example.

  • One of the submitted answers is even more interesting (and ridiculous). It was created via some PHP-MySQL wizard websites. Although the result works fine (of course!), he does not receive any credit because his programming skills could not be proven.

So far, the best answer scores 60%. I don’t think this is an exciting result. If you found this useful, please let me know, thanks!

–Derrick

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Today, I had a discussion with my co-worker on the best languages for web applications. While I argued that Perl, and Ruby performs better than PHP, my co-worker had an opposite opinion. He believed that PHP is the best language overall because it is widely used. It brings me to think of a question, does the most popular imply the best?

Let’s answer this question by examples:

Category Most Popular The Best Why The Best?
OS (Desktop) Windows OS X User friendly, secure, stability, and performance.
OS (Server) Linux, Windows Server FreeBSD Fast, stable, secure, simple design, and centralize management.
Browsers Internet Explorer, Firefox Safari Fast, secure, stable
Programming languages (Desktop/GUI) C#, Java C, C++ Fast, secure
Programming languages (Web/Server) PHP, ASP Ruby, Python, Perl Fast, fewer lines of code.
Database MySQL, Oracle Berkeley DB, Tokyo Cabinet Fast I/O, simple design, smaller size of the database file.
Software company to work for Microsoft Start-up Rewards, opportunity to grow

I think there are several reasons why the most popular things are not the best.

1. Most popular thing is always backed by the best marketing strategies. Marketing strategies is simply a way to let people know about the product and convince them to use it. It has nothing to do with the quality of the product at all.

Example: The ads of Internet Explorer 8 look very attractive. Is it the most secure browser ever?

2. Most people are followers. They are not good in selecting good products from bad products(i.e., filtering the noise). They believe that the choice form most people (most popular) should be the best one. This is similar to election. The choice of most people is more likely to be better.

Example: Is MySQL really the best database?

3. Different people have different preferences. So a popular product must have the general taste. For example, an extremely hot and spicy food may be better to the body, but it is not as popular as a mild one, because the number of people that can take extremely hot and spicy food is smaller.

Example: Linux is very easy to configure comparing to FreeBSD (GUI vs command line) from the end-user perspective, but it is less powerful and stable overall.

Conclusions:

Think twice before your move.

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I was looking for a good way to convert a number to the Excel column letter, for example:

1 -> A
26 -> Z
27 -> AA
28 -> AB
800 -> ADT

etc.

After searching on Google, I could not find any algorithm I want. (The closest one can handle up to two letters, i.e., ZZ. It will crash if the number is too large.). So I ended up creating my own.

Basically, you can think of this problem as a 26 based number conversion. Here is the php version. It should be pretty simple to convert it to a different language. Let me know if you have any problem.

function columnLetter($c){

    $c = intval($c);
    if ($c < = 0) return '';

    $letter = '';
             
    while($c != 0){
       $p = ($c - 1) % 26;
       $c = intval(($c - $p) / 26);
       $letter = chr(65 + $p) . $letter;
    }
    
    return $letter;
        
}


Usage:
columnLetter(1303618093);    //DERRICK

Note that if you prefer lower cases rather than upper cases, you can simply replace 65 by 96 in the code.

Enjoy~!

–Derrick

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