Comments on: Those Crazy Interviewers!

By: Will Parker

Will Parker — Sat, 16 Sep 2006 09:18:22 +0000

I got asked the standard "how do you move a mountain" chestnut.

"So, I have a budget in the billions?" Yes. "The mountain is in the US?" Yes. "The test for a moved mountain is ...?" The highest point on the mountain must correspond to the new location and the peak cannot be moved separately from the rest of the mountain.

"How far do I have to move it?" 10 meters east.

Easy peasy.

Hire minions to covertly track down everyone with direct administrative control over the USGS topographic database.
Using the unlimited budget, bribe the senior members of that group to set the recorded GPS coordinates for all USGS survey points within 25 kilometers of the mountain peak 10 meters east. (Accompanied by whiteboard graphics in three colors.)
For each USGS survey marker within the range 25 to 75 kilometers from the mountain peak, modify the recorded GPS coordinates to smoothly deform the orihginal coordinate grid to disguise the modifications made in Step 2. (More whiteboard magic in a fourth color.)
Repeat Steps 1-3 for the land resource organizations in the states and/or provinces containing any part of the grids described Steps 2-3.

..............................

Preliminary project estimates: 60 days, $5-20 million direct costs (minions), $1.5 to $4.5 billion 'consultation' fees depending on location of target mountain.

That ended the interview cycle. I think I won the job on deviousness-plus-style points.

By: Michael Maniscalco

Michael Maniscalco — Tue, 18 Jul 2006 13:02:52 +0000

Oh, I remember this puzzle. My solution, for anyone who is still interested, was placed at http://www.michael-maniscalco.com/lucky sevens/luckySevens.htm

The source code also included a hand C++ 128 bit class. It isn't super fast, but it fit the need regarding this puzzle.

I think the time required was less than 0.0001 seconds or so on my 3GHz machine if I remember correctly.

By: Steve

Steve — Sat, 20 Aug 2005 05:49:00 +0000

Mine took about 18 minutes on a reasonably fast machine. It wasn’t brute force, but I guess it wasn’t that clever either. I’d be interested to know the algorithm that could give you the answer in less than a second.

By: Nodem

Nodem — Wed, 17 Aug 2005 21:26:00 +0000

FairDice, I didn’t spend too long thinking about the math, so I went for brute force. Mine took 7 hours!

By: FairDice

FairDice — Wed, 17 Aug 2005 00:57:00 +0000

Oh good — I got that same number for the sevens problem (indeed, found this page because it’s the only hit for Googling on it); nice to get confirmation of the answer.

Mine took 15 lines, but in my defense, it ran in 0.09 seconds. I’m kind of disappointed that they made the upper bound just low enough that it’s feasible to do it by brute-force calculation; it should be 100 trillion instead of 100 billion. (Then the sum would be, um, 102041179796115463104759635, an 87-bit integer [0.13 sec].)

By: Nodem

Nodem — Fri, 12 Aug 2005 22:46:00 +0000

Back in the dot com days I was asked to write a fibonacci program by a 20 year old interviewer (he was the CTO).

I did the Lucky Sevens with seven lines of code and got: 102,049,428,685,193,293,045.

Watch out though, this number needs 67 bits unsigned (you can’t fit it into 64 bits).

By: Sergio

Sergio — Tue, 09 Aug 2005 04:06:00 +0000

I once interviewed for Microsoft in Mexico. They asked the standard cannibal/monk variation problem (this particular incarnation included the U2 members with a flashlight), which I — stupidly — couldn’t solve until about an hour after the interview, when I had stopped thinking about it.

They also asked me to make a fast program for computing prime numbers.