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How to implement PICK'S theorem in c++
By v-O_O-v, history, 5 years ago, In English

Hello! I am unable to find any resource on implementing pick's theorem for a polygon in c++. Can anyone suggest me a site or code where i can understand it.

Thanks.

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5 years ago, # |
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Well Pick Theorem states that: S = I + B / 2 - 1 Where S — polygon area, I — number of points strictly inside polygon and B — Number of points on boundary.

In 99% problems where you need to use this you are given all points of a polygon so you can calculate S and B easily

Polygon Area
Points on boundary

So by having S and B you can get I using some simple maths: I = S + 1 - B / 2

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    5 years ago, # ^ |
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    I did not understand how you found boundary points. Can you explain in detail.Photon_

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      5 years ago, # ^ |
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      So points with integer coordinates on line segment is GCD(dx,dy) + 1

      Where GCD is Greatest common divisor, dx is distance between x coordinates of points, dy — is distance between y coordinates of points

      Why?
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    5 years ago, # ^ |
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    ats+=abs(__gcd(dx,dy)) - 1;

    That -1 should not be there.

    EDIT: Ah sorry I missed the = A.size(), it works out fine, my bad.

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    4 years ago, # ^ |
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    what happens if vertices of polygon don't have integer coordinates? how to handle that case?

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      4 years ago, # ^ |
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      It also works for rationals, and all the numbers you can read are rational ... you can maybe multiply them by $$$\frac{1}{\epsilon}$$$. with $$$\epsilon$$$ the minimum $$$10^{-k}$$$ value that you can work.

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5 years ago, # |
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(https://www.google.com/amp/s/www.geeksforgeeks.org/count-integral-points-inside-a-triangle/amp/)

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