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Tech-Interview Riddles
An anonymous submitter writes "A computer engineering student at UC Berkeley has made a comprehensive archive of riddles from technical interviews. Very challenging and loads of fun. Also useful for interview preparation."
for more tech interview questions and answers try http://www.techinterview.org/
What's up with using this type of question for interviews, anyway? Sure, they can be fun, but they're perfectly useless as far as telling whether someone can actually write solid code. 9 times out of 10, all they tell you is whether the interviewee has heard that one before.
To interviewers: Do you really think that the answers to these questions don't spread through the entire department within 15 minutes after your first interview? I realize that "knowing the answer" makes you feel smarter than the prospective employee in some sense, but how about actually doing your job for a change?
I used to put this one on my programming tests. It's actually shocking how many people get it wrong...
You are writing a parser that reads a C program and translates all the variable names into new names of the form "VAR######", where ###### is an integer incremented for each unique variable name. Discuss what is needed for the case where the C program already contains a variable of the form "VAR######".
Sometimes it's best to just let stupid people be stupid.
My first thought was, where are the answers. My second thought was, thank god I have a job.
"Karma can only be portioned out by the cosmos." -Homer Simpson
A man would like to have safe sex with three women, any of whom may be carrying an STD. Given two condoms, how can he do so, while ensuring that no STD is passed from one woman (or possibly himself) to another (or to himself)?
This is a common situation on the job. Who says riddles aren't relevant in interviews?
"What will it say in the newspaper about you when you die? In effect, write your own obituary:"
All-time best answer:
"Gunman shoots nine, then self."
My friens Marc *swears* he said this in an interview.
Cheers,
Jim in Tokyo
-- My Weblog.
You have a monopoly in a given market. A company creates a groundbreaking product and establishes a new, completely different market. Assuming you cannot buy the company, how do you smash it and extend your monopoly in the old market to the new one?
How would you go about designing an email client that executes any code that is sent to it?
If you could remove any of the fifty states (thus rendering federal antitrust statutes inapplicable to corporations in that state) which state would you remove and why?
How would you go about designing an operating system for people who hate computers and who just want to use their machines for pay-per-view entertainment?
An End User License Agreement (EULA) appears in a window with "I Agree" and "I Disagree" buttons. The text area in which the EULA appears is eighty columns wide. How many lines of text can be included in the EULA before a computer that just meets your system requirements is unable to load it into memory?
At a fork in the road between two cities, you see 2 people. One always tells the truth, and comes from the city of safety. The other person always lies and comes from the city of cannibals, where they will eat you. Which one do you hire to write up licensing agreements for your legal department?
An Arab sheikh is old and must will his fortune to one of his two sons. He makes a proposition. His two sons will use their computers, and whichever computer gets a blue screen of death first will win the fortune for its owner. During the race, the two brothers do nothing on their computers, neither willing to risk a blue screen of death. In desperation, they ask a wise man for advice. He tells them something; then the brothers immediately jump onto the computers and start installing new hardware, sharing files, and downloading hastily written security updates. What did the wise man say?
"So there's a programmer writing some code, in C. That programmer needs to use a buffer to store some data. How does the programmer write the code such that an unexpectedly large amount of data doesn't overwrite the stack and result in a remote root exploit?"
Because the holes are round.
I mean, really, any other shape wouldn't fit...
*ducking*
My video compression blog
Am I the only one who thinks this interviewing technique is retarded?
Because Microsoft does something most definitely isn't a reason to emulate it. Microsoft isn't exactly known for producing well designed software, nor software that reuses proven patterns or algorithms that solved known problems 20 years ago. Better to hire a bunch of 21 year old college grads who can solve word problems from 8th grade algebra, and pretend that Microsoft invented computers! Whee.
When I hire developers I want them to be good developers, not promising young interns. My interview questions typically involve technology questions, process questions, some theoretical PROGRAMMING questions, and some social / communication questions. I'm not saying that hiring smart people is a bad idea, but ignoring skills and only looking at generic problem solving ability is a recipe for unbelievably bad code. It's like hiring musicians based on measured hearing sensitivity and reflexes. OK, maybe that matters if you want to figure out which 5 year old is going to be a prodigy, but hand them an instrument and the noise that comes out is going to sound like ASS.
Examples of things that "smart" developers I've worked with before have totally missed:
- the existence of more efficient data structures than arrays
- generalizing code into reusable chunks (functions, objects, whatever)
- regular expressions
- the difference between "client" and "server"
- the reason for using descriptive variable names
- collection libraries with built in sorting ("whatcha workin' on?" / "coding up a quicksort algorithm" / "in a J2EE app!?!?")
You can't just get this from reading a book, either, although that definitely helps. You have to have some degree of EXPERIENCE too: at least a few projects, and some awareness of things like performance tuning, security, coding for maintainability, etc.
I would use these "tech interview questions" only for hiring interns or recent college grads where the expectation is zero experience, zero clue, zero skill, and a correspondingly low salary. After all you're investing in someone. But for someone that commands a market rate developer salary in the high five figures, screw the brain teasers - just spend a couple of hours grilling them on skills, experience, discipline, etc. They will respect you big time in return because they know when you extend an offer that they won't be working with a bunch of dumb-asses who can get the explorers across the river without being eaten by the headhunters but who can't code their way out of a soggy paper bag.
I did a lot of interviews at MS when I was there, and I quickly learned not to ask riddles. First off, it makes people who don't get them uncomfortable and angry. Second, it doesn't actually show that the person can write software.
I used a much simpler approach, so simple most people think its silly. But thats the point; nobody leaves the interview thinking they were tricked or duped. I always started with implementation of strcpy(). Half of the candidates failed right there! They took most of the hour to get it right (or not), but were able to see point-blank that they were not ready for the job.
Next, I would ask about crashing cases, and if they figured out overlapping memory locations, have them write a 'fixed' version. This weeded out another big chunk. After that, I went into some color counting algorithms.
I stayed well withing the field of what the candidate would expect, and did not try to trick him or make him nervous with off the wall riddles.
This approach worked great, and didn't leave anyone feeling robbed and abused. The ability to solve riddles *is* an indicator of how smart the person is, but it is *not* an indicator of how good a programmer they will be.