The running time of the recursive sort method (Program ) is given by
where n is the number of elements in sequence to be sorted, is the running time of the selectPivot method, and i is the number of elements which end up to the left of the pivot, .
The running time of sort is affected by the selectPivot method in two ways: First, the value of the pivot chosen affects the sizes of the subsequences. That is, the pivot determines the value i in Equation . Second, the running time of the selectPivot method itself, , must be taken into account. Fortunately, if , we can ignore its running time because there is already an O(n) term in the expression.
In order to solve Equation , we assume that and then drop the s from the recurrence to get
Clearly the solution depends on the value of i.