quick sort

quicksort.rb

def quicksort(array, from=0, to=nil)
  # Sort the whole array, by default
  to = array.count - 1 if to == nil

  # Done sorting
  return if from >= to

  # Take a pivot value, at the far left
  pivot = array[from]

  # Min and Max pointers
  min = from
  max = to

  # Current free slot
  free = min
  while min < max
    if free == min # Evaluate array[max]   
      if array[max] <= pivot # Smaller than pivot, must move
        array[free] = array[max]
        min += 1
        free = max
       else
        max -= 1
      end
     
     elsif free == max # Evaluate array[min]
     
       if array[min] >= pivot # Bigger than pivot, must move
         array[free] = array[min]
         max -= 1
         free = min
        else
         min += 1
        end
       else
         raise "Something went wrong..."
       end
       
    end

    array[free] = pivot

    quicksort array, from, free - 1
    quicksort array, free + 1, to
end

a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15].shuffle
# Quicksort operates inplace (i.e. in "a" itself)
# There's no need to reassign
quicksort a
puts "quicksort"
puts a