// Returns a list of all subsets of the given set A that contain k elements.
function subsets(A, k) {
  let combinations = [];

  function _subsets(set, length) {
    if (length === set.length) {
      combinations.push(set);
      return;
    }

    for (let i = 0; i < set.length; i++) {
      let copy = set.slice(0);
      copy.splice(i, 1);
      _subsets(copy, length);
    }
  }

  _subsets(A, k);

  return combinations;
}