askhelper's blog

Help for POI 2018 Round #1 problem: Stone
By askhelper, 6 years ago, In English

Hello, all! I need your help for this problem. Basically, we have n vectors originated in (0, 0) and we are to find a subset of these vectors such that length of their sum is maximum.

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6 years ago, # |
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Try to think about some optimal solution (and some final point). Which vectors should we use to reach this point?

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    6 years ago, # ^ |
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    That makes me think about some kind of dp. For example, if the answer is (x, y) then we need to get $$$(x, y)$$$ or $$$(x - a[1].x, y - a[1].y)$$$ from the vectors 2 to n.

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      6 years ago, # ^ |
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      What I'm trying to suggest is that the chosen vectors in the optimal solution have some specific property. Finding this property should later lead to a pretty straightforward solution.

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