Boboge's blog

USI(University of Lugano) team selection 2023-2024 in gym.
By Boboge, history, 12 months ago, In English

Hi everyone!

Today, our university had run our team selection round. All problems are prepared by me.

Special thanks to Tobo, Duck_sajin, Kyooma, zbceyond, Hile_Meow, gongkoufadongji, Joler_ and jiubei for testing.

The contest is now uploaded to the Codeforces gym at USI-Team-Selection 2023-2024.

I hope you can enjoy the problems!

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12 months ago, # |
  Vote: I like it +8 Vote: I do not like it

How A

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12 months ago, # |
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good problems

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11 months ago, # |
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How to prove B?

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    11 months ago, # ^ |
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    Reflect the point $$$(x_2, y_2)$$$ "across" the river, ie. replace with $$$(x_2, -y_2).$$$ If you pick a point $$$p$$$ on the river to go to then distance from $$$p$$$ to $$$(x_2,y_2)$$$ is the same as distance from $$$p$$$ to $$$(x_2,-y_2).$$$ Then by triangle inequality (shortest distance between two points in the plane is the straight line segment between them), so you just choose $$$p$$$ so that $$$(x_1,y_1),p,(x_2,-y_2)$$$ are collinear and the minimum distance is just the distance between $$$(x_1,y_1)$$$ and $$$(x_2,-y_2).$$$

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