4 ms·

Pretty sure 13 minutes isn't possible. The constraints are: no more than two people on the bridge at a time, they have to walk together to share the necessary f

Pretty sure 13 minutes isn't possible. The constraints are: no more than two people on the bridge at a time, they have to walk together to share the necessary flashlight, and if someone doesn't have the flashlight, they can't cross. i.e., if the 1 minute and 10 minute people cross first, it takes both ten minutes to cross. Afterwards, the 2 and 5 minute people are stuck without the flashlight, so before they can cross, someone has to carry the flashlight back to the other side. It is a bit of a puzzle, but it's not really a very good one.

daleharvey 17y ago
yeh realised just after posting I was being dumb (sending the 10+5 then imagining the 1 guy comes back ... I was tired)
- aduric 17y ago
  Ya, pretty sure 17 is not possible. Unless you can turn off the flashlight on the way back?
sailormoon 17y ago
It's not a good puzzle at all - I kept on trying to think of the "trick" which would somehow make it faster than just the fastest person acting as the relay for all the other parties, but that really does seem to be the solution.
- Karzyn 17y ago
  There actually is a faster solution. Using the relay method: People Minutes 10 & 1 10 1 11 1 & 5 16 1 17 1 & 2 19 Best solution (that I know of): 1 & 2 2 1 3 10 & 5 13 2 15 1 & 2 17
  - sailormoon 17y ago
    Ha! So there is a trick. Good thinking. Guess that's why I don't work at Microsoft .. :/
    - camccann 17y ago
      An excellent demonstration of why it's a bad puzzle--there's an obvious naive solution that most people get stuck at (the 19 minute one), and a single critical insight that reveals the otherwise simple optimal solution. It's not testing logical reasoning ability; both solutions are "obvious", which one depending on if you know the trick. It's not testing creative problem-solving; the solution is so constrained by ridiculous limitations that there's only one "correct" answer. It's not testing skills for any sort of practical, real-life situation (I hope). The main thing that questions like this reveal is whether or not the interviewee enjoys frivolous puzzles and riddles. Not the worst thing to select candidates based on I suppose, but probably not ideal, either...

daleharvey 17y ago

yeh realised just after posting I was being dumb (sending the 10+5 then imagining the 1 guy comes back ... I was tired)

aduric 17y ago
Ya, pretty sure 17 is not possible. Unless you can turn off the flashlight on the way back?

sailormoon 17y ago

It's not a good puzzle at all - I kept on trying to think of the "trick" which would somehow make it faster than just the fastest person acting as the relay for all the other parties, but that really does seem to be the solution.

Karzyn 17y ago
There actually is a faster solution. Using the relay method: People Minutes 10 & 1 10 1 11 1 & 5 16 1 17 1 & 2 19 Best solution (that I know of): 1 & 2 2 1 3 10 & 5 13 2 15 1 & 2 17
- sailormoon 17y ago
  Ha! So there is a trick. Good thinking. Guess that's why I don't work at Microsoft .. :/
  - camccann 17y ago
    An excellent demonstration of why it's a bad puzzle--there's an obvious naive solution that most people get stuck at (the 19 minute one), and a single critical insight that reveals the otherwise simple optimal solution. It's not testing logical reasoning ability; both solutions are "obvious", which one depending on if you know the trick. It's not testing creative problem-solving; the solution is so constrained by ridiculous limitations that there's only one "correct" answer. It's not testing skills for any sort of practical, real-life situation (I hope). The main thing that questions like this reveal is whether or not the interviewee enjoys frivolous puzzles and riddles. Not the worst thing to select candidates based on I suppose, but probably not ideal, either...