How many uses for a brick could you come up with in a minute? Now imagine that you're being interviewed for a job that you badly want and have just been asked that question. That's only the tip of what it's like trying to get your foot in the door at the 25 most difficult companies to interview with. Each year, job information site Glassdoor runs an extensive analysis on users' ratings of their job interviews and picks the 25 companies known for the most difficult interviews. The data came from 170,000 reviews of interviews that users had gone on. The site users rate the difficulty, whether the experience was positive or negative, how many days the process ran, and sample questions. The question about a brick -- actually a common question to test someone's creativity -- was used at semiconductor company Nvidia, No. 20 on the list. That's right, it can get much tougher. Glassdoor has compiled this list for the last three years and each time consulting firm McKinsey & Company was at the top, with an average difficulty rating of 3.9 out of 5. The full interview process takes about 39 days, with 77 percent of the interviewees reporting a positive experience and 12 percent, a negative one. The second and third toughest were Thoughtworks and Boston Consulting Group. Out of the top 25, Paycom had the highest percentage of negative experiences, compared to the average of 13 percent, according to Glassdoor. The most popular companies, based on positive experiences, were Rolls-Royce and Avaya, which tied at 86 percent. The average of positive experiences was 52 percent. Although the average interview process for all companies rated on Glassdoor was 16 days, some of the difficulty for the top 25 may be how long it takes to get through the process. The average for them was just over 31 days. The longest were at Teach for America (55 days), Procter & Gamble (50 days), and Rolls-Royce (46 days). Here come the questions: A business analyst candidate interviewing at McKinsey got the question, "How would you calculate the annual carbon emissions from electric versus gas vehicles in the EU?" The easy answer would seem to be that electric vehicles don't emit carbon because they don't burn fuel or have exhaust. However, the electric power has to be generated somehow, and that will involve some amount of emissions. (Non-profit International Council on Clean Transportation wrote a 24-page paper trying to answer that question.)  Many tough questions, such as "describe a time when you had to do something you didn't want to do" (Proctor & Gamble brand manager interview) or "what kind of people do you dislike the most?" (Stryker sales representative interview) are intended to reveal something about the character of the person being interviewed. Others, like estimating the revenue from ticket sales to the 2012 Olympics (Bain & Company business analyst interview), are intended to see how a person thinks and approaches problems. Some measure specific job knowledge and skillsets. Happily, the days of the gotcha trick question may have started to wane. This was something that was once synonymous with Google. But the company realized that "brainteasers are a waste of time," as Laszlo Bock, senior vice president of people operations at Google, told The New York Times.  How many golf balls can you fit into an airplane? How many gas stations in Manhattan? A complete waste of time. They don't predict anything. They serve primarily to make the interviewer feel smart.  From Google's lips to interviewers' ears.  Whole Foods is known as an ethical company when it comes to its food, from locally-sourced produce to lovingly raised chickens. But its heart extends to its employees too, giving them a better starting pay than their competitors and encouraging them to move up.  Looking for a job at Whole Foods? Start your search here.  Darden Restaurants is a curious find on this list, since the parent company of casual eating favorites Red Lobster, Olive Garden, The Capital Grille and LongHorn Steakhouse has been sued repeatedly by employees for wage theft, discrimination and other alleged sins. But it seems that many employees are more than happy on the job, including 135,000 part-timers, Fortune points out, to whom Darden offers low-cost health insurance.  Looking for a job at Darden Restaurants? Start your search here.  "You will want to make a career here," says a current Marriott employee in enterprise operations. By most accounts, Marriott is just incredibly well-run: open and encouraging management, reasonable policies, great pay and benefits, superb discounts on hotel rooms for family and friends. On the downside, working for a major hotel chain means sometimes working weekends and holidays, and moving to a new town if you want to climb the ladder.  Looking for a job at Marriott International? Start your search here.  "I enjoy coming to work every day and I have a lot of best friends at work," wrote a current Stryker engineer on Glassdoor.com. And while some employees gripe that they're slightly underpaid, everyone gushes about the drive and integrity of their co-workers. Fortune notes that the medical device manufacturer also tries to keep the culture fun with ping pong tables and "pie-your-manager" contests.  Looking for a job at Stryker? Start your search here.  For a company so large, American Express offers its employees an impressive level of flexibility, according to reports on Glassdoor.com, including the opportunity to work evenings and weekends or from home. The financial services firm also has won numerous accolades for its commitment to diversity.  Looking for a job at American Express? Start your search here.  "Fast paced and performance based," writes a Devon Energy senior systems administrator on Glassdoor.com. "You are very well rewarded for delivering and meeting your goals." And that's in addition to the top-of-the-line salaries and benefits at this Oklahoma City-based oil and gas producer. And like many of the companies on this list, the openness of the C-suite sets it apart. Fortune reports that President and CEO John Richels sometimes calls up employees to thank them for good work.  Looking for a job at Devon Energy? Start your search here.  Employees at the oil and gas exploration and production company, from geologists to truck drivers to IT support, enjoy an extensive benefits package, including a 401(k) match of up to 15 percent. Workers at the Oklahoma City campus say it's beautiful, and that its onsite restaurants are remarkably good. Employees also enjoy regular bonuses, and in 2011, 8,000 of them received $8 million in bonuses simply for following safe practices, Fortune reports.  Looking for a job at Chesapeake Energy? Start your search here.  This electronics company has made it onto Fortune's best-companies-to-work-for list for years, in addition to winning accolades for its training opportunities and the leg up it offers interns and entry-level staff. Employees on Glassdoor.com say the work is cutting edge, the benefits generous, and the culture welcoming, although perhaps not as hip as other tech firms.  Looking for a job at Qualcomm? Start your search here.  At this data storage company, "everything just works," says one former senior analyst on Glassdoor.com. That includes training opportunities, time off to volunteer, competitive salaries, and flexibility. Others praise how accessible the executives are, and Fortune reports that Vice Chairman Tom Mendoza calls 10 to 20 employees into his office everyday to personally thank them for their work. Looking for a job at NetApp? Start your search here.  There's nary a best-place-to-work list that Google hasn't topped. The perks of working at the world's most popular website, including free gourmet sushi and free haircuts, have become the stuff of legend. So much so that it's subject of an upcoming movie starring Owen Wilson and Vince Vaughn.  Google is even developing a new mega-campus, so perfectly designed that every employee will purportedly be able to work by natural light, without any glare on their screens. In fact, the only thing that employees seem to complain about is that all the employees are so amazing that they're too amazing for their jobs.  Looking for a job at Google? Start your search here.  Erik Sherman is a widely published writer and editor who also does select ghosting and corporate work. Follow him on Twitter at @ErikSherman
Job site Glassdoor released its annual list of 25 companies known as having the toughest interview processes and some sample tough questions