class2018F.txt

9  1  3  6  5  2  5  10
pivot = [x[0] + x[7]) / 2 = 9
i                 j
5  1  3  6  5  2  9  10
                  ij

quicksort(x, left, right)
if (right - left < 2 )
  return
i = left
j = right
pivot = (x[left] + x[right]) / 2
while (i < j ) {
      while (x[i] < pivot && i < j)
      	    i++;
      while (x[j] >= pivot && i < j)
	    j--;
      if (i < j)
         swap(x[i], y[j]);
}
quicksort(x, left,  i-1)
quicksort(x, i, right )


same thing as pseudocode...
while i < j
  while x[i] < pivot
     i <-- i+1
  end