Given a number n, create an n-by-n matrix in which the integers from 1 to n^2 wind back and forth along the rows as shown in the examples below.
Examples:
Input n = 3
Output a = [ 1 2 3
6 5 4
7 8 9 ] Input n = 4
Output a = [ 1 2 3 4
8 7 6 5
9 10 11 12
16 15 14 13 ]
Solution Stats
Problem Comments
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16 Comments
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13 older comments
Mandeep Singh
on 14 Jun 2013
nice one
André
on 24 Jun 2014
good one
ABDELRAHMAN
on 12 Dec 2015
i got same solution on matlab, but i don't know why i didn't here
Samarth Shivaswamy
on 28 Dec 2015
I am no expert, but does anyone else think that the first test case is flawed? "%%n = 4;" instead of " %% (new line) n = 4;" So, "n" is never defined for the first case. Am I right? If not, I apologize!
shahin rmz
on 29 Oct 2016
that seems legit
Aniket Patil
on 7 Mar 2017
nice one
UnCroissant
on 7 May 2017
Really enjoyed this one.
Loris Chavée
on 17 Jul 2017
Can someone help me? My solution works on my matlab but gives me an error during the test! What am I supposed to do ? :(
Kyle Chappell
on 8 Nov 2017
I think the answer to test suite 5 should be c = 2 since the first row is 0.21 and the second is 0.26. Please correct me if I'm wrong.
Lányi György
on 13 Mar 2018
Awesome!
christopher Minix
on 24 Apr 2018
Awesome
Majid Farzaneh
on 17 May 2018
Great
Shizun Li
on 31 Oct 2018
Check this out.
function b = back_and_forth(n)
b=1:n^2;
b=reshape(b,n,n)';
for i=2:2:n
b(i,:)=fliplr(b(i,:));
end
end
Sharon Spelt
on 8 Nov 2018
It appears a '\r' is needed after the %% in the first test of the solution to make it process properly.
goc3
on 9 Nov 2018
The problem with the first test case has been fixed here.
Aleksandrov Igor
on 14 Jan 2020
This code
b=vec2mat(1:n^2,n)
b(2:2:end,:)=fliplr(b(2:2:end,:))
work in Matlab, why it doesn't works on site?
Solution Comments
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1 Comment
Shizun Li
on 31 Oct 2018
Check this out.
function b = back_and_forth(n)
b=1:n^2;
b=reshape(b,n,n)';
for i=2:2:n
b(i,:)=fliplr(b(i,:));
end
end
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1 Comment
Thomas Pingnam
on 15 Nov 2017
my code works on my PC but not on this..
a = [1:(n^2)];
a = reshape(a,[],n)'
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2 Comments
Peng Wang
on 29 Aug 2017
How can u do it in 10
Maruf Ahamed
on 21 Apr 2018
I also want to know.
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1 Comment
Yoshimasa Nakatani
on 15 Jan 2017
I can't write shorter program.
(^.^;)
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1 Comment
SIVAPRAKASH DANABALASINGAM
on 10 Jan 2017
very easy
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1 Comment
TAYALAN SIVALINGAM
on 29 Dec 2016
gj
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2 Comments
Tomas Macha
on 2 Oct 2016
Why is this not working please?
a = ones(n,n);
for i = 1:n^2;
a(i) = i;
end
a = a'
I've tried this in school and it worked fine... :O Could you please help and explain? :)
Allen
on 10 Oct 2017
Look closer at the requirements. Even rows should be flipped, such that their values are in descending order when reading from left-to-right.
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1 Comment
pranju chakrapani
on 11 May 2016
Why is this problem showing errors in line 6 when I have a code of 4 line?
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2 Comments
qloreyze ueyzzyyc
on 24 Aug 2015
It works on matlab
ABDELRAHMAN
on 12 Dec 2015
i got same solution on matlab, but i don't know why i didn't here
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1 Comment
Gnaneswar Nadh satapathi
on 5 Dec 2013
good Question
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1 Comment
dariodazio
on 11 Aug 2013
really clever :)
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4 Comments
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1 older comment
Pedro
on 28 Apr 2013
Sorry for the nasty solution. I'm hoping the use of str2num and anonymous functions will eventually be limited, since most simple problems can be solved with this cheat.
Florent Hennart
on 22 May 2013
Hi,
Could you comment how using str2num and anonymous functions decreases the score from 46 to 13? Is it a glinch in the notation system?
Regards
Pedro
on 23 May 2013
Hi, Florent.
The scoring in Cody is based on the number of nodes in the parse tree, and strings only require one node.
You can have a look for yourself by typing:
'>> mtree('back_and_forth.m','-file').show'.
Try to do it for the same code, without str2num, and you'll see that even small things like parenthesis or plus signs require their own node in the tree.
In terms of performance, the two versions are not so different. The problem here is that every solution, that use str2num in this way, will have the same Cody score, regardless of how elegant or efficient the anonymous function is.
arcturus
on 24 May 2013
I really like how you've split the matrix into two. That's a clever insight! And I am really interested in knowing WHY str2num requires only one node.
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2 Comments
Shuang-Wei
on 6 Jan 2014
brilliant!
niu
on 28 Feb 2014
clever!
abs(sort(-cumprod(-ones(n)).*reshape(1:n^2,n,n)',2));
This one is more clear.what do you think?
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1 Comment
sea knowledge
on 13 Dec 2012
well done,why can't come up with this method
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1 Comment
Nigel Davies
on 3 Aug 2012
Sorry, I just applied a slightly involved ans trick to the previous best solution. I hurts me though that the best solution involves a for loop.
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1 Comment
prithvi
on 15 Feb 2012
This should work
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1 Comment
Jan
on 27 Jan 2012
This is faster and nicer than calling an external function to flip the direction.
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