packList.js

function packLists(a) {
  if (!a.length) {
    return [[]];
  } else if (a.length == 1) {
    return [[a[0]]];
  }


  var c = [a[0]]
    , b = [c]
    , k = 0;

  for (var i = 1; i < a.length; i++) {
    if (a[i] != a[i - 1]) {
      k++;
      b.push([]);
    }

    b[k].push(a[i]);
  }

  return b;
  
}