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.