CRNCombinatorics.cpp

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/* Copyright 2008-2014 INSA Lyon
 * 
 * This file is part of libcrn.
 * 
 * libcrn is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * libcrn is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with libcrn.  If not, see <http://www.gnu.org/licenses/>.
 * 
 * file: CRNCombinatorics.cpp
 * \author Jean DUONG
 */

#include <CRNMath/CRNCombinatorics.h>

using namespace crn;

int Combinatorics::CountCombinations(int n, int p) noexcept
{   
    if ((p == 0) || (p == n))
    {
        return 1;
    }
    
    if (p == 1)
    {
        return n;
    }
    
    return (CountCombinations(n - 1, p - 1) + CountCombinations(n - 1, p));
}

int Combinatorics::CountArrangements(int n, int p) noexcept
{
    if (p > n)
    {
        return 0;
    }

    int Arr = 1;
    
    for (int k = n - p + 1; k <= n; k++)
    {
        Arr *= k;
    }
    
    return Arr;
}