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oremj/gist:276428

Created January 13, 2010 18:23
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gistfile1.hrl
-module(combin).
-export([factorial/1, combination/2, prob15/1]).
factorial(N) -> factorial(N, 1).
factorial(1, Acc) -> Acc * 1;
factorial(N, Acc) -> factorial(N - 1, N * Acc).
combination(N,K) -> factorial(N) div (factorial(K) * factorial(N - K)).
prob15(X) -> combination(X * 2, X).
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