Generate combinations from a given set.

combinations.cpp

#include <vector>
#include <stdint.h>
#include <iostream>

template <typename Iterator>
inline bool next_combination(const Iterator first, Iterator k, const Iterator last)
{
    /* Credits: Thomas Draper */
    if ((first == last) || (first == k) || (last == k))
        return false;
    Iterator itr1 = first;
    Iterator itr2 = last;
    ++itr1;
    if (last == itr1)
        return false;
    itr1 = last;
    --itr1;
    itr1 = k;
    --itr2;
    while (first != itr1)
    {
        if (*--itr1 < *itr2)
        {
            Iterator j = k;
            while (!(*itr1 < *j)) ++j;
            std::iter_swap(itr1,j);
            ++itr1;
            ++j;
            itr2 = k;
            std::rotate(itr1,j,last);
            while (last != j)
            {
                ++j;
                ++itr2;
            }
            std::rotate(k,itr2,last);
            return true;
        }
    }
    std::rotate(first,k,last);
    return false;
}

void main(){
    // 5-choose-3 
    std::size_t n =184;
    std::size_t k = 3;

    std::vector<int> ints;
    for (int i = 0; i < n; ints.push_back(i++));

    do
    {
        for (int i = 0; i < k; ++i)
        {
            std::cout << ints[i] << " ";
        }
        std::cout << "\n";
    }
    while(next_combination(ints.begin(),ints.begin() + k,ints.end()));
    std::cin.get();
}