Fast Combinations in C++

combinations.cxx

#include <algorithm>
#include <iostream>
#include <vector>

// Another incredible bit of C++ code
// https://stackoverflow.com/a/28698654/338107
// 
// change std::vector<bool> for std::array<bool, N> to
// make your compiler work hard

void comb(int N, int K)
{
    std::vector<bool> bitmask(K, 1); // K leading 1's
    bitmask.resize(N, 0); // N-K trailing 0's

    // print integers and permute bitmask
    do {
        for (int i = 0; i < N; ++i) // [0..N-1] integers
        {
            if (bitmask[i]) std::cout << " " << i;
        }
        std::cout << std::endl;
    } while (std::prev_permutation(bitmask.begin(), bitmask.end()));
}

int main()
{
    comb(5, 1);
    comb(5, 2);
    comb(5, 3);
    comb(5, 4);
}