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Find nCr mod p when n, r, p are large
I want to find nCr(n choose r, if you will) modulo a prime. The trouble is that all the numbers i.e. n, r and prime are large and are of the order of 10^9.
One method I could come up with is computing each of the three factorials individually(using FFT and multipoint evaluation) but that seems too tedious. It may also timeout.
Is there anything else I can do ?
