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Number of ways to choose k from a multiset
By secomo, history, 3 years ago, In English

Example : {1,2,2,3,3}

the answer here is 5 :

{1,2,2} {1,2,3} {1,3,3} {2,2,3} {2,3,3}

I want a formula to calculate this.

I searched through Internet but I did not find a clear answer.

I am not good at math so I want a simple explination If that is possible. Thank you.

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3 years ago, # |
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Helppppp Plssss

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3 years ago, # |
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451E - Devu and Flowers

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3 years ago, # |
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https://cses.fi/book/book.pdf Page 72 (Of the book, not pdf) . Slightly change the algorithm and it should work

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3 years ago, # |
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here is a beautiful solution from aops using generating functions. I don't know generating functions too much, but I understood the solution.

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