Exercise 7.2.3

Show that the running time of QUICKSORT is $\Theta(n^2)$ when the array $A$ contains distict elements and is sorted in decreasing order.

In this case PARTITION always returns $p$ because all the elements are greated than the pivot. While the if will never be executed, we still get one empty partition and the recurrence is $T(n) = T(n-1) + \Theta(n)$ (even if its body is not executed, the for is still $\Theta(n)$).