1%%% Copyright (C) 2009 Enrique Marcote, Miguel Rodriguez
2%%% All rights reserved.
3%%%
4%%% Redistribution and use in source and binary forms, with or without
5%%% modification, are permitted provided that the following conditions are met:
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8%%%   this list of conditions and the following disclaimer.
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11%%%   this list of conditions and the following disclaimer in the documentation
12%%%   and/or other materials provided with the distribution.
13%%%
14%%% o Neither the name of ERLANG TRAINING AND CONSULTING nor the names of its
15%%%   contributors may be used to endorse or promote products derived from this
16%%%   software without specific prior written permission.
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29-module(cl_stats).
30
31%%% EXTERNAL EXPORTS
32-export([combinations/2]).
33
34%%%-----------------------------------------------------------------------------
35%%% EXTERNAL EXPORTS
36%%%-----------------------------------------------------------------------------
37combinations(M, N) when (M >= 0), (N >= 0), (M >= N) ->
38     div_factorial(M, N) div factorial(M - N).
39
40%%%-----------------------------------------------------------------------------
41%%% INTERNAL FUNCTIONS
42%%%-----------------------------------------------------------------------------
43factorial(0) ->
44    1;
45factorial(N) when N > 0 ->
46    N * factorial(N - 1).
47
48
49div_factorial(M, N) when N > M ->
50    0;
51div_factorial(M, M) ->
52    1;
53div_factorial(M, N) ->
54    M * div_factorial(M - 1, N).
55