Problem 46. Which doors are open?

Created by Cody Team

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5170 Solutions
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Last Solution submitted on Jan 14, 2022

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Jan on 27 Jan 2012

The description does not match the example: The point 3 should be "3. On the # trip down the alley, start with door # [and process every #-th door]".

David Young on 3 Feb 2012

I agree with Jan - the description is not clear. The final instruction should be "return the list of open door #'s", presumably.

David Young on 3 Feb 2012

If the description was clearer, I'd give this problem a "like", because a good solution depends on a good analysis of the problem more than on just neat coding.

Ned Gulley on 1 Mar 2012

Sorry about the confusion. I tried to clarify the problem description.

Mattias on 4 Jan 2015

Nice problem! The explicit solution was very surprising to me once I found it.

Michael on 9 Feb 2015

Classic problem--unfortunate that the test suite reveals the punchline.

Justin Pinkney on 28 Jan 2016

Yes I initially thought y = sum(open doors)

Jerivington on 2 Jun 2016

good problem, easy solution once realising how to solve

Sanzhar Askaruly on 17 Jun 2019

easy if to think a bit

Solution Comments

Solution 2288134

1 Comment

1 Comment

Ali Osman Üstünel on 17 May 2020

good

Solution 727419

2 Comments

2 Comments

Peng Zhiyun on 2 Sep 2015

though I did not understand the question...

Andrea Nigro on 15 Sep 2020

the problem are not clear, could you explain me?

Solution 449250

1 Comment

1 Comment

Alexander Razmyslov on 26 Mar 2015

Very nice solution without for loop

Solution 267741

1 Comment

1 Comment

Preeyanka on 26 Jun 2013

Problem isn't robust to direction of vector

Solution 156433

1 Comment

1 Comment

Claudia on 16 Nov 2012

Genius!

Solution 137317

2 Comments

2 Comments

Sebastian on 8 Sep 2015

Nice explanation. I just derivated the formula from the solution ;-)

Jiawei Gong on 19 Feb 2020

Thanks for the explanation.

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Problem 46. Which doors are open?

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