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Graham Scan: Background & Python Code

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Code below… In this video we’ll learn about the Graham Scan, an algorithm developed in the 70s, used to construct ‘Convex Hulls’. Before we delve into the details of the algorithm, we’ll first learn a bit ‘Convex Hulls’ themselves, and some ways of testing to see if a set of points constitutes a ‘Convex Hull’. Towards the middle of the lesson, we’ll switch over to our coding editor and actually implement the algorithm in Python (2.7).
►Code for this lesson: github.com/bfaure/Python_Algo...
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► Python Data Structures: • Python Data Structures
► GUI development in Python (WIP): • Python GUI Video Tutor...
References:
[1] en.wikipedia.org/wiki/Convex_...
[2] en.wikipedia.org/wiki/Convex_...
[3] • Video
[4] www.geeksforgeeks.org/convex-h...
[5] en.wikipedia.org/wiki/Graham_...
End song is “Out of the Skies Under the Earth” by Chris Zabriskie

Опубликовано:

28 ноя 2017

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Комментарии : 23

@joaogoncalocouto 3 года назад

Amazing video and explanation! I’m a subscriber after this one

@xt3988 5 лет назад

Great video!

@qzorn4440 5 лет назад

very interesting python code. thanks.

@BenAllwoodtheGreat 4 года назад

Great Video!!!

@jamshidali4912 3 года назад

This is Awsome

@Weth767 3 года назад

Great!

@owaissultan40 3 года назад

Awesome

@syedqaisarali9644 3 года назад

plz sir make video on concave Hull By the way this video is very helpful for me

@miguelpetrarca5540 2 года назад

What is the intuition/need behind applying secondary sort by distance and having point closer to anchor be sorted before point farther from anchor

@Toopa88 4 года назад

You can also use this in the console: for x in {1..5}; do python main.py; sleep 1; done Or something like: time for x in {1..5}; do sleep 1; done Instead of sleep 1 you would put your program, but here it would take about 5 seconds. My output: real 0m5.122s user 0m0.000s sys 0m0.078s Not sure if this helps anybody but sometimes I find it useful.

@jiageng1997 5 лет назад

Thank you for the video! However, when I run the GitHub script such as in 13:15, the plot GUI freezes at the first frame. I am only trying 10 points.

@jiageng1997 5 лет назад

It also produces IndexError: list index out of range for rather small sizes (eg >300)

@sophiar.2310 6 лет назад

GitHub code comments say " polar_angle " function returns the polar angle (radians) from p0 to p1, while your video says its from p1 to p0. So which one is right?

@BrianFaure1 6 лет назад

+Sophia R. Hello Sophia, I apologise for the confusion, the angle returned is from p1 to p0, so the angle from the 0° axis to the point p0, treating p1 as the origin of the 0° axis.

@sophiar.2310 6 лет назад

Got it. Thanks! Great channel, definitely learnt a lot here. It would be nice to cover dynamic programming and greedy algorithm in the future!

@BrianFaure1 6 лет назад

+Sophia R. Thanks so much, I'll add those to the queue!