selectNth
Selects the nth element from the given list after partially sorting it based on a mapping function.
This method modifies the input list to reorder its elements such that the nth element is placed at the correct sorted position if the list were fully sorted according to the provided mapper.
Return
The nth element in the reordered list.
Parameters
items
The list of elements to process and partially sort.
n
The zero-based index of the element to select after partial sorting.
mapper
A lambda function that maps an element of type T to a Double, used to determine sorting order.