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ITA Software's Hiring Puzzles

• roundsquare 16y ago
  I'm curious, how useful to people think these kinds of puzzles are in hiring?
  • mfr 16y ago
    To use a recent movie quote: "If you can dodge a wrench, you can dodge a ball." ITA's business is all about dealing with fiendishly clever transforms on small-ish sets of data, and the results are needed Right Now. Most of the hiring puzzles revolve around that theme. Much like any other company giving these kinds of problems, it's not about bringing out that cleverness every day, but it's about figuring out who has the ability to think in that way, along with the persistence to work on the problem until it's done.
    • kmak 16y ago
      I agree with the concept, but at some point it became trivia, which kills the point.
    • wallflower 16y ago
      Classic ITA paper that shows you the complex problems they deal with: http://www.demarcken.org/carl/papers/ITA-software-travel-complexity/ITA-software-travel-complexity.pdf http://www.demarcken.org/carl/papers/ITA-software-travel-com...
  • ynniv 16y ago
    They produce more false negatives than false positives. If you aren't in a hurry to grow, thats a good thing. Even "cheating" (memorizing the techniques) to the point of being able to solve a problem on site (which is part of the interview) is not trivial.
    • jules 16y ago
      What do you mean by false negative?
      • jimfl 16y ago
        false negative = filtering out good candidates false positive = allowing bad candidate to pass
        • WildUtah 16y ago
          False negative = Type I error False positive = Type II error
    • yesimahuman 16y ago
      Like you said, these problems filter out the people who would be great for getting stuff done and helping you build your software quickly (i.e. more practical people who find these problems a bother). But perhaps you don't always want that kind of person. Personally, I find these problems interesting but the one I liked the most was the instant search because it had an element of user interaction rather than mere algorithmic problem solving, so I guess I might be the one filtered out :)
      • Psyonic 16y ago
        I solved the Instant Search problem when I was applying there for an internship. The puzzles aren't required for internships, but I figured it could only help, and I landed the internship. Was a great experience! For my solution, I tried both tries and hash tables, and I found them to perform at more or less the same level. I later experimented with suffix trees, which I think is probably the best way to go for that problem.
  • raffi 16y ago
    I never liked the practice of hiring puzzles. I love coding useful things. Working on a hiring puzzle feels like jumping through hoops which is something I prefer to avoid.
    • hugh3 16y ago
      Perhaps, but did you notice that one of the puzzles actually involves scraping through ITA's own database to find round-trip flights to Chicago? That seemed like a good touch, asking the interviewee to replicate a small part of ITA's own functionality so they could understand the magnitude of the problem. Actually it sounds like a pretty easy problem from this far out, but maybe if I actually worked on it I'd discover it was trickier than I thought.
      • raffi 16y ago
        Sounds cool, I'd gladly do something like that if they were paying me. I think a good solution is to define a well-scoped project and bring candidates on board on a contract basis to implement them. This contract basis project can even be done remotely. This offers the candidate a chance to learn about you, you can learn about the candidate, and in the end you can both decide what is best for you.
• bartwe 16y ago
  Dunno if they are good for hiring, but some look fun to try for a little hobbying.
• chime 16y ago
  Yesterday someone mentioned the Sling Blade Runner problem from their archives and I can't stop thinking about it. * http://www.itasoftware.com/careers/puzzle_archive.html?catid=39#Sling%20Blade%20Runner http://www.itasoftware.com/careers/puzzle_archive.html?catid... * http://stuffthathappens.com/blog/2007/10/03/sling-blade-runner/ http://stuffthathappens.com/blog/2007/10/03/sling-blade-runn... I'm in the middle of writing a web-based anagram server and there's some similarities in both these problems. You have a dictionary that you iterate through recursively to find a solution. For anagram, the solution is usually found with 3-5 recursions (100 word list, 3 recursions: 100^3 calculations - not a big deal for desktop software, too slow for web-app). For Sling Blade Runner, your goal is to keep increasing the depth of the recursion as much as possible so it's actually impossible to go through 100^200 calculations. Does anyone have any idea if these problems could be better tackled by converting them to map-reduce problems? I'd like to play with Amazon's mapreduce service. Edit: Neat. I came across: http://blog.xebia.com/2009/07/02/thinking-mapreduce-with-hadoop/ http://blog.xebia.com/2009/07/02/thinking-mapreduce-with-had...
  • brown9-2 16y ago
    Are you looking to pre-generate the results or generate them dynamically? I think MapReduce will only be effective for the former.
    • chime 16y ago
      There are no map-reduce implementations that work in real-time? I thought Google search worked like that. I do want it to work dynamically.
      • brown9-2 16y ago
        MapReduce is used to build the search index (constantly), and your searches are run against the index. You might find some of these links useful: http://wiki.apache.org/hadoop/ProjectDescription http://wiki.apache.org/hadoop/ProjectDescription http://wiki.apache.org/hadoop/HadoopIsNot http://wiki.apache.org/hadoop/HadoopIsNot
      • 16y ago
• eru 16y ago
  I like " Decrypting the Two-Time Pad (hard!)" (http://www.itasoftware.com/careers/puzzle_archive.html?catid=39#Decrypting http://www.itasoftware.com/careers/puzzle_archive.html?catid... the Two-Time Pad)
• kaddar 16y ago
  I was about to graduate graduate school, I had finals, final papers, and interviews. I had 2 companies which had hiring puzzles, and interviewed at 5 companies. I was really interested in ITA, unfortunately I couldn't schedule in the time to work on the hiring puzzle within the 2 week window this occurred. I sort of imagine that these puzzles have an outlier effect: it removes the top and bottom users from a selection pool. Maybe that's okay, personally I was a bit disappointed at the missed opportunity. One way they could improve this is by giving the puzzles expiration dates, removing the fear of completing one far ahead of the interview process, and having it expire. You'll still miss out on those who haven't heard of ITA until the near-graduation career fairs, but it will at least improve the situation.
  • sokoloff 16y ago
    Why do you think this would have adverse selection against the top of the pool? I can clearly see how it would act a barrier to application for the bottom candidates (a good thing for the company), and I can see how it would reduce the number of applicants who are applying "everywhere they can think of" (also probably good for the company in terms of getting a more qualified [in the sales-conversion-rate sense] base of applicants). In my experience, the very top of the applicant pools aren't applying to a particularly large number of places.
    • kaddar 16y ago
      Although the top tier candidates may not be applying at many places, they are receiving many more first, second, or even third interviews. Thus, their timing is tight in a two week window near the end of school when they start receiving offers. Near-Bottom-tier candidates may receive less interviews and are incentivized to perform more desperate acts in order to receive interviews, and thus have more time for puzzle-based applications. But as I said, it's not too big of a deal, if they would only post ahead of time how long puzzles would be active, so one could complete them before this tightly-timed period.
• r00k 16y ago
  I've tackled one of ITA's puzzles (word rectangle, I think I found a 7x7 in 60-ish seconds). I got through a phone screen and interview, but was ultimately turned down for 'lack of experience.' If you're trying to get hired at ITA by solving one of these puzzles, here's something to keep in mind: the point of solving a puzzle is to GET A PHONE SCREEN. That's all. Many of these puzzles have no 'perfect solution.' I'd be surprised if any of them do. Instead, they're a proving-ground for your coding chops. So write tests, write comments, and make the code as clear as you can. Provide your best solution, but remember: the point is to write something good enough that they'll pick up the phone and CALL YOU. I spent much too long on my solution before I realized it was already good enough to clear this bar. If you do get an interview, plan for a full day. You'll get another problem of this nature (though much simpler) at the end of the day, plus the usual salvo of whiteboard coding exercises.
  • rman666 16y ago
    I've been working on the word rectangle problem, too. Care to share your '7x7 in 60-ish seconds' solution? Or at least some hints on how you approached the problem? I'd be much obliged, as they say.
    • r00k 16y ago
      One word: tries.
    • gradschool 16y ago
      I agree that tries are good. There is also an 8x8 solution if you wait long enough. Strangely there don't seem to be any non-square solutions up to the sizes I was able to check, so you might as well search only for squares, which speeds it up a lot. I'm not sure if I should post a solution but I'm happy to email it to you.
  • dfranke 16y ago
    I disagree with this advice. My bitvector solution was memorable enough that I spent a good portion of my in-person interview discussing it (it took advantage of multiple cores even during parsing, and had some passages of hand-written assembly in order to exploit SSE2). A good-enough solution will be good enough to get you in the door, but an excellent solution may carry you further.
• pge 16y ago
  In the past, ITA seemed to be focused on Lisp. I hadn't looked at the puzzles in a number of years, but the newer ones seem focused on Java. Anyone know if that signals a change at ITA? A move from Lisp to Java? Perhaps more customer-facing code? In any case, their puzzles are always good for a brain workout.
  • strlen 16y ago
    ITA still uses Common Lisp. There are excellent blog entries on this matter by Dan Weinreb: <http://danweinreb.org/blog/category/ita-software> http://danweinreb.org/blog/category/ita-software>. However, they don't require Common Lisp knowledge from new hires. The beauty of Common Lisp is that there really is very little syntax to learn. Afaik, the simply use the excellent Practical Common Lisp book by Peter Seibel as a "training manual". The problem with Common Lisp, unfortunately, is there's no standard and cross-implementation way to create an application that makes heavy use of network I/O, multi-processing/multi-threading and the file system. That's would not be a problem internally at ITA (where must have built a standard set of libraries), but it would be a problem for taking submissions for web applications from applicants. On the other hand, even making a complete end-to-end webapp is a part of the Java standard. I am guessing that's why the puzzles that require talking HTTP either to or from a web server require Java. Several of their other puzzles, however, don't specify a programming language (e.g., bit vector, word rectangle) and could probably be very well suited to being done in a Lisp.
• mukyu 16y ago
  Years ago when I was still in high school I somehow stumbled upon these and tried a few out (the one with the one time pad and the movie titles). I certainly was not ready to tackle them at the time, but even when failing I learned a lot. Years later I ran into a paper on finding the shortest path in a directed graph with negative cycles and it reminded me of all of my attempts to do the same. It is a shame they don't have a post-mortem after they retire the problems. I really enjoyed reading the break down of one of them ( http://conway.rutgers.edu/~ccshan/wiki/blog/posts/WordNumbers1/ http://conway.rutgers.edu/~ccshan/wiki/blog/posts/WordNumber... ) even though I did not attempt it.