function quicksort(q)
     var list less, pivotList, greater
     if length(q) = 1 {
         return q
     } else {
         select a pivot value pivot from q
         for each x in q except the pivot element
             if x < pivot then add x to less
             if x = pivot then add x to greater
         add pivot to pivotList
         return concatenate(quicksort(less), pivotList, quicksort(greater))
     }