help with combinations !!!!

[ayan_2587]

hi frndz....

i was wondering that given
1<n<1000000 &
1<r<1000000

how do i efficiently find nCr (combination) for any given values of n & r.

please help with an efficient algorithm...

[MK27]

Forgive my ignorance of mathematics but it would seem to me this does not any algorithm.

{r,n}

[aside:] For some silly reason cboard's vBulletin believes everything in braces is code...unless you are new and want to paste a few hundred lines

[stevesmithx]

As nCr would be factorial(n)/(factorial(r)*factorial(n-r)) I guess it boils down to finding the factorial efficiently.
If an approximate solution would be okay, then go for http://en.wikipedia.org/wiki/Stirling%27s_approximation