(function (n) {

  // n -> [a] -> [[a]]
  function comb(n, lst) {
    if (!n) return [[]];
    if (!lst.length) return [];

    var x = lst[0],
      xs = lst.slice(1);

    return comb(n - 1, xs).map(function (t) {
      return [x].concat(t);
    }).concat(comb(n, xs));
  }

  // f -> f
  function memoized(fn) {
    m = {};
    return function (x) {
      var args = [].slice.call(arguments),
        strKey = args.join('-');

      v = m[strKey];
      if ('u' === (typeof v)[0])
        m[strKey] = v = fn.apply(null, args);
      return v;
    }
  }

  // [m..n]
  function range(m, n) {
    return Array.apply(null, Array(n - m + 1)).map(function (x, i) {
      return m + i;
    });
  }

  var fnMemoized = memoized(comb),
    lstRange = range(0, 4);

  return fnMemoized(n, lstRange)

  .map(function (x) {
    return x.join(' ');
  }).join('\n');

})(3);