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Number of ways to choose k from a multiset if order matter
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.
