Generating N choose K Permutations in C++ [duplicate]

Answer 1

You output first k members of every n! permutations. 4! = 24 permutations. First two permutations are

1,2,3,4
1,2,4,3

and you have got 1,2 and 1,2

To get combinations (4,2), you might, for example, use vector

 {0,0,1,1}

permute it, and output indexes of 1's