How could i shorten my for loop code?

2016 9 27
1 个回答
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更新时间：2016 9 29
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0 个投票

I made a script to print out a diamond, but would like to make my script shorter. Only for loops are allowed. Is there a different logical way that could eliminate some for loops?
Here is the code:
row=input('enter an odd number: \n');
for i= 1:ceil(row/2);
for j=1:row-i
fprintf(' ')
end
for k=1:2*i-1
fprintf('*')
end
fprintf('\n')
end
for j=ceil(row/2)-1:-1:1
for q=1:row-j
fprintf(' ')
end
for k=2*j-1:-1:1
fprintf('*')
end
fprintf('\n')
end
%this is what it prints:
row= 9
*
***
*****
*******
*********
*******
*****
***
*
Also, the index logic could probably be simpler. Thanks!

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José-Luis
José-Luis 2016-9-27

1 个投票

numRows = 25
numStars = [1:2:numRows,numRows-2:-2:1];
numSpaces = (numRows - numStars) / 2;
If you really want a loop:
for (ii = [numStars;numSpaces])
spacePrint = repmat(' ',1,ii(2));
starPrint = repmat('*',1,ii(1));
fprintf([spacePrint,starPrint,'\n']);
end

3 个评论
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Dan Po
Dan Po 2016-9-27
That works. Would you know if there is a way to merge the two ' * * ' sections in the code? I am at a beginners point of thinking, and am scrubbing my newbie brain for a solution, but have come short.
What I did was print line by line of spaces and *, and print line by line with the loop.
Also, at what point did you learn the tools for this solution method?
So far what I am not familiar with is repmat, ii, and organizing matrices like you did, but I will look into those things.
Thanks for your time.
for i= 1:ceil(row/2);
for j=1:row-i
fprintf(' ')
** end
** for k=1:2*i-1
fprintf('*')
end
fprintf('\n')
end
for j=ceil(row/2)-1:-1:1
for q=1:row-j
fprintf(' ')
** end
** for k=2*j-1:-1:1
fprintf('*')
end
fprintf('\n')
end
José-Luis
José-Luis 2016-9-27
My pleasure. Seeing (and trying to understand) how other people do it is a good way to learn. I guess that's how I learned most of what I know now. It just takes time.
In don't understand what you mean by merge the two sections.
Dan Po
Dan Po 2016-9-29
What i meant is is there a way to consolidate these two for loops (the starred lines)?
for i= 1:ceil(row/2);
* for j=1:row-i %used to print spaces on one line
* fprintf(' ')
* end
* for k=1:2*i-1 %used to print stars on same line
* fprintf('*')
* end
fprintf('\n')
end
I dont think there is. My for loop does what your repmat does. So far i could reduce my code by using your style of index increment then decrement as so:
before: for i= 1:ceil(row/2);
and: for j=ceil(row/2)-1:-1:1
-------------------------
after: for i= [1:(row+1)/2,(row-1)/2:-1:1]
This reduction leads to my code being 2 lines longer than your code. You win this time... Lol.
Also, it seems like your code could be reduced to a super short:
numRows = 3 % input('enter something');
matSpaceStar=[[1:2:numRows,numRows-2:-2:1];[numRows-[1:2:numRows,numRows-2:-2:1]]/2];
for ii = matSpaceStar
fprintf([repmat(' ',1,ii(2)),repmat('*',1,ii(1)),'\n']);
end
Earlier, were you hinting that there is a shorter way to make the shape than using a for loop?
If you could spare more time, could you tell me?
I thought about it, but have run out of time and need to get back to homework. This problem is pretty fun.
Thank you for your help!

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