Sounds like the same number appears at least twice in a box no? Did you implment a check on boxes?

I like how c++ allows you to write unbearable code...
What I don't like though is that modular arithmetic returns negative numbers...

I'm quite happy I was able to solve this without translating the input string to another variable type...

Don't know if it's the heat of the summer or what but this kata got me stuck for a little while. I won't look at elevators the same way indeed ;-)

Really nice!
You know a good kata when you find new edge cases after every fix.
And also when you have to re-write the program 3 times from scratch.

Really nice kata! I had fun refactoring my solution while going up from «Skyscapers 4x4»

Best practice hey :D
Nice Kata, I can't wait to tackle the 7x7 version, but I suspect that a lot of optimisation has to be done…

I'm still amazed by these kind of solutions and each time I wonder : "Is this person a thousand times more clever than the rest of us? Or does he/she spends 4 * time on the problem studying its ins and outs in order to find the most compact and obscure algorithm..."

The error handling…
This one was harder than expected, writing it while learning to type in Dvorak made it even harder :)

My god when I see that some of you solved it with so little code, when it took me 3-4 days to come up with this solution, well I feel stupid :)
This solution barely makes it below timeout, but at least I learned a lot about map, reduce, partial, iterators.
Thank Bubbler for this wonderful problem.
EDIT : line 6 is useless, i was trying something and didn't delete it.

I start to understand it. Wonderful kata. Thanks Bubbler, you made my day.
Well I have not solved it yet, but soon :)

Sorry I didn't mean to sound obnoxious. I was kind of disapointed to solve it this fast. Perhaps forbid the use of imports such as "fractions", that would bump the difficulty a whole lot.

This was waaaay too easy for a 4 kyu. I usually spend at least 4 hours to solve a 4 kyu. This took me 15 minutes.

Wow, this was difficult... (2 days)
I wanted to go with an ugly 10 lines solutions with lots of modulos and conditionals, but finally I found it easier to isolate some cases in sub-functions.
My advice : use verbose variable names to keep your code readable and do not hesitate to split the problem in sub-functions even-though it is not necessary.