Shoelace creative solution for Area of a Convex Polygon by veky - python coding challenges

Enable Javascript in your browser and then refresh this page, for a much enhanced experience.

Shoelace solution in Creative category for Area of a Convex Polygon by veky

def checkio(d):
    a,(u,v)=0,d[-1]
    for x,y in d: a,u,v=a+x*v-y*u,x,y
    return abs(a)/2

May 24, 2013

Comments:

veky on May 24, 2013, 10:29 p.m.
Determinant approach (shoelace formula).

bryukh on May 25, 2013, 11:55 p.m.
Interesting solution.

lesenv on Dec. 1, 2013, 9:15 p.m.
<pre class='brush: python'> for x,y in d: a,u,v=a+x*v-y*u,x,y </pre> clever, clever! i had to look twice to get it. nice :)

veky on Dec. 1, 2013, 9:22 p.m.
Only twice? Wow. :-D

lesenv on Dec. 1, 2013, 9:27 p.m.
yes twice. the other solutions were working with the determinant, this is similar. nice, that you are using that you renew 3 vars at the same time!

veky on Dec. 1, 2013, 9:29 p.m.
<blockquote> yes twice. the other solutions were working with the determinant, this is similar. </blockquote> It is no secret, look at the lowest comment. ;-) <blockquote> nice, that you are using that you renew 3 vars at the same time! </blockquote> Yeah, I usually use zip with shifted sequence, here I wanted something more exotic. ;-)

spoty on July 28, 2014, 7:55 p.m.
Nice! Thanks for bringing up Shoelace formula.

veky on July 29, 2014, 10:33 a.m.
You have a weird definition of "bringing up". This was written more than a year ago. :-D

spoty on July 29, 2014, 1:27 p.m.
For me it was just 17 hours ago :P

znatny_kulish on Jan. 10, 2017, 8:29 a.m.
sum of areas of triangles using det/2 formula? am I right?

veky on Jan. 10, 2017, 1:22 p.m.
The <a href="https://en.wikipedia.org/wiki/Shoelace_formula">title</a> is suggestive... :-)

znatny_kulish on Jan. 10, 2017, 1:42 p.m.
the formula itself is based on a geometrical sense of determinant (area of parallelogram which is double area of a triangle). The trick is in signs of sub-determinants (for convex shapes they are all positive or all negative - depends on we are searching clockwise or not), for non-convex shapes sub-det's might be of different sign.

veky on Jan. 11, 2017, 12:39 p.m.
Yes, of course. It's all well known, I think. :-)

hao.daniel on May 31, 2019, 8:12 p.m.
Another Wow! Maybe we need a category for the "Shortest code Solutions" too.. ;-)

veky on May 31, 2019, 8:41 p.m.
Even without that category, we get too many pointlessly short solutions. The shortness should be the consequence, not the main motivation. :-!

hao.daniel on May 31, 2019, 11:02 p.m.
Agreed. Sometimes, people abuse the power of Python expressiveness to a dangerous degree that making the 'code maintenance' a nightmare.

veky on June 2, 2019, 10:16 a.m.
I'd like to point out that this mostly occurs on game sites such as this one. In professional coding, people usually know what's readable ('maintainable' is a different criterion, and much rarer achieved, simply because it's very context-dependent).

Dropbox

0 %

PyCharm The Python IDE for Professional Developers. Enjoy productive Python, web and scientific development with PyCharm. Download it now!