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I want a fast algorithm to calculate no of permutations for n elements with some elements identical.

Using formula :

n! / k1! k2!....km!

where ki = no of i elements, i = (1,2,...m)

and k1 + k2 + ...... + km = n

**Without calculating each factorial** as if n is a large no like 400, 400! goes out of range of long long int( largest possible size in c++ ).

If you are posting code please use c/c++.

Thanx in advance :)